No experience with the Gaia but I do own and can recommend the Roland JD-Xi, the Korg Minilogue, the Waldorf Blofeld and the Studiologic Sledge.
Each one has its own personality and I love them all but if you are looking for a first time investment in a serious synth I'd say the Sledge has the most potential as a playable instrument.
All of these sell in the same price range as the Gaia. The sledge prices in highest at $899 to $999 USD but it boasts a full sized 5 octave Fatar keybed with channel aftertouch and the ability to tweak every parameter with single function knobs and switches so not too much deep menu diving at all.
Gary