It seems most people that play one petsite also actively play at least one other.
I personally don't play Neopets anymore, but I actively play Aywas and Ichumon. I recently joined Flightrising, but I haven't really done much there, just breed and sell them babes.
One good thing about Aywas and Flightrising is they have cross-site trading. I have never done it, but it seems to be pretty big if you play across multiple sites that allow it. I share an account on Aywas with someone and she is constantly earning money on Flightrising, just to sell on Aywas for that currency. Its pretty nifty!
Ichumon doesn't have a lot of active members currently, but of all the petsites I've played, its the one I've played the most. The battling is great.
I remember botting the hell out of Ichumon! I made the first and maybe the only auto-battler. It walked around and automatically fought monsters. Never got caught from it, but when they started doing wars, I made a war battler version of it and that's what got me banned. The program made me uber uber rich but after getting banned once, I didn't see any fun in starting over.
I thought this program was too good and kept it all for myself.
I feel like there are a few people on site that auto-battle, or at least was. One got banned for leaving it on ALL day while afk (which was dumb xD) and the other self-banned (dunno why)
Lack of staff activity right now, on-site. Admin busy IRL and the other Admin is.. I dunno
i play leopets. its pretty much a rip off of the old neopets. i like it because you can pretty much make a pet with any name you want and they have the old art. but the only way to make leopoints is luck. or to be really good at codebreaker and play that for hours on end. or "restocking" which is done by buying items from shops that have a higher value than you bought them for and selling to the grundo warehouse. actual restocking isnt very profitable because theres such a small userbase and the only really profitable items are ones used for kadding, which anyone that kads usually gets them from the shops themselves.
i mostly play for the nostalgia of the older art style.