Nano Pals are great.
I've mainly only had Nano Puppy's but they're really fun. Released in the first wave of virtual pets (late 90s), they were quite popular. PlayMate Toys (the brand that makes them) re-released them in around 2005. No internal changes were made, though. Still, a great virtual pet.
You can either get a Puppy, Kitty or Baby. You could get various other things (such as a horse) after the initial release of the Puppy, Kitty or Baby, but the original is always the best. You look after the pet as it grows up.
I really like it because they made it with a standard background, but it had a pixellated background that would change. You'd see the pet or baby walking outside, past a fence, a lamp and other stuff. When it went to sleep, if you had the puppy, for example, you see it in a kennel etc.
Overall, I really loved my Nano Puppy. I still have it, but I haven't ran it in a while. I've been meaning to buy a new one but time (and money) has got the better of me!
But yeah, I'd recommend a Nano Pal.
Read about them here:
https://www.tamenagerie.com/nano.html