The ARP - I'm an ARP Fetishist so I specifically like those sounds. It does do more than stereotypical ARP sounds...but that's where it eats lightning and craps thunder!!! Mini-Keys are a plus for me, I've seen people complain about those though. I love the Ring Mod on it so much!!!
The GAIA - Think of it like a supped up CASIO and less like a synth. I do like mine...but I like it the way people love their children (well I guess they're here so whatever ) It's not a great synth. I kind love shitty synths sounds though so the GAIA really scratches that itch. So again, I like it but would never recommend one. They retailed at $700 when they came out and that is kind of crime against humanity. I paid $350 for mine and still feel like I overpaid . It also was my 'first synth', it's light, and it does not take up a lot of space so I can deal with it. Plus, I would feel kind of bad pawning it off on someone (kind of like herpes). The thing completely shits the bed on low end (not a good thing).