Although you sent me a PM with this question, I'm answering you in this thread so others can read and chip in.
A Few Opening Remarks
(1) Since I've never played either one of those keyboards, I can't recommend either one based on personal experience. My comments below are mostly of a general nature.
(2) This sort of question comes up repeatedly, so a few years ago someone in this forum (Skipp?) wrote a series of posts which were collected into six articles:
https://www.keyboardforums.com/forums/buying-a-keyboard.85/
The six articles should be read in the opposite order from how they're listed on the page-- i.e., start at the bottom ("Which Keyboard Should I Buy?") and work your way up to the top ("Keyboard Prices"). While the articles don't cover the two keyboards you specifically mentioned, and some of the information is a little outdated-- after all, the articles were written about four years ago, and keyboard manufacturers march on-- they will give you an idea of the things to consider when looking to buy a keyboard.
(3) When you ask somebody "I'm thinking of buying either A or B, which do you think I should get?" you're setting yourself up to be disappointed-- well, maybe you'll be happy with the choice that someone else makes for you, but there's also a good possibility you'll be unhappy with their choice. The best thing to do is to thoroughly research the choices yourself, narrow them down to the most likely candidates, try out the likely candidates if that's possible, then decide for yourself which one to choose.
Some General Comments and Questions
(1) Yamaha or Casio-- which company makes better keyboards? A lot of people will tell you that Yamaha makes better keyboards, and that Casio keyboards sound like cheap toys. I'm not going to take sides in that debate. My first electronic keyboard (not counting my old Farfisa Matador organ) was a Casio CTK-710, which I still have. It doesn't have a large selection of sounds by today's standards, and some of them do sound rather "unconvincing" to put it mildly-- but I think some of them sound pretty good, especially considering how inexpensive it was. My nephew has a Casio WK-110, which is a newer model but not the newest, and it sounds better than my old CTK-710. Today's Casio keyboards are much improved over yesteryear's.
When I dug out my old Casio a few years ago, I decided it was time to buy a newer keyboard, and I chose to get a Yamaha-- not because I didn't like Casio, but more for the sake of variety. After researching the models in my price range, I went with the PSR-E433 and have been happy with it. I even bought a PSR-E443 earlier this year. But I can't really compare my Yamaha keyboards to my Casio keyboard, because the differences in their ages and abilities are too great. I do think that my Yamaha keyboards sound a bit better than my nephew's Casio, but I haven't heard the newest Casio keyboards.
One thing I'll say is that Casio's keyboards seem to have more features for less money than comparably-priced Yamaha keyboards-- e.g., the CTK-7200 is only $100 more than the PSR-E443, but it has some features that the PSR-E443 doesn't.
(2) Do you want to be able to modify the keyboard's sounds? When I first started thinking about buying a Yamaha keyboard a few years ago, one of the things I really wanted was the ability to modify the sounds by tinkering with the attack/release, cutoff/resonance, and reverb/chorus settings. This made my choice pretty clear-- the PSR-E433, which in some ways is more like a synthesizer than just an electronic keyboard. It even has a pitch-bend wheel, but not a modulation wheel. If you don't care about these features, then the PSR-E343 should be okay, because it doesn't have them. But if you think you might like to modify the sounds, then I'd recommend that you consider the PSR-E443 rather than the PSR-E343.
On the Casio side, the CTK-6000, CTK-6200, CTK-7000, and CTK-7200 have pitch-bend wheels and tone-editing capabilities, but if you don't need that then the CTK-4200 might be adequate. Note that some of the Casio keyboards also have sliders for drawbar organ sounds, so that's another thing you might consider.
(3) Do you want a generic keyboard, or one that's tailored more for Indian music? Both Casio and Yamaha have Indian versions of some of their keyboards, which have some Indian instrument sounds and styles that aren't included in the generic keyboards. Casio has the CTK-810IN, CTK-850IN, CTK-6300IN, and CTK-7300IN. Yamaha has the PSR-I425 and the PSR-I455. I'm not sure, but I think the Indian versions are more expensive than the generic versions, so if money is a major factor then you might want to go with a more generic model. But if the Indian instruments and styles are important to you, then go for one of those models if you can afford it.
(4) Do the number of keys matter? If you want a 76-key model, or even an 88-key model, then the Yamaha PSR keyboards won't do, since they have 61 keys-- you'll want to look at some of the other Yamaha lines instead. Likewise, if you want a 76-key Casio then you should look at the WK line rather than the CTK line-- or the digital piano lines if you want 88 keys.
(5) Don't forget the VST instruments! Even if you buy a "lesser" model Casio or Yamaha that doesn't have as many instrument voices or styles as a more expensive model, you can still use it as a MIDI controller with VST instruments-- it might not have a lot of "control surfaces" for controlling the VST instruments, but you could control things with a tablet, laptop, or desktop computer.
What Do You Want, and How Much Can You Pay?
When it comes to buying a keyboard, you can think of it like buying a car-- hopefully not nearly as expensive, but the point is that you should buy something you think you'll be happy with for a long time. You don't want to end up regretting your choice, wishing you'd gone with a different brand or model. You also want something you can grow into, that will still be able to give you musical pleasure and empower your creativity even after you've owned it for a few years.
So the first thing you need to do is decide how much you can afford to spend on your new keyboard. I'd recommend setting two different price limits-- the most you'd prefer to pay, and the absolute highest price you're able and willing to pay if you can't get what you want at your preferred limit. Also, keep in mind that you'll probably want to buy additional things like a keyboard stand, a dust cover, maybe a sustain pedal, maybe an amp, and things like that-- so don't forget to factor those things into the cost.
Once you determine how much you can spend, I'd recommend making a list of all the models that fall within your price range. Look at their basic features and cross off any models that don't have the features you want. Then go to the web sites of the manufacturers and download the owner's manuals for the models that look the most promising. Do the features work the way you'd like, or does it seem like they'll be hard to use, etc.? And once you've narrowed things down to two or three likely candidates, see if you can try them out in a music store to see if you like the way they sound and feel. If that isn't possible, at least search on YouTube for any videos where people are demoing the keyboards, so you can get an idea of how they sound.
It's not for me to decide which keyboard you should get, but if the Indian instruments and styles are important to you then I'd recommend a Yamaha PSR-I455 or PSR-I425 rather than a PSR-E343-- or else one of the Casio Indian models, CTK-810IN, CTK-850IN, CTK-6300IN, or CTK-7300IN-- depending on the price, availability, features you want, sounds, and other personal preferences.
Sorry I can't give you a simpler, more decisive answer, but it's your money and satisfaction at stake, not mine, so you need to decide for yourself.
