Yeah - love fish, but there's a reason that I ended up giving away my tank when my fish were gone - I do not have enough money to get the set-up that I ideally want and weekly tank cleans are a pain (although not too taxing on the muscles - you just have to syphon half the water out whilst giving the gravel a hoover and then slowly add the water back in at the right temperature xP )
Yeah, fish are always seen as the easy option 'cause there isn't really any legislation to protect pet fish, so stores and companies are happy to promote the myth and sell tanks that are far too small (it's a hard sell to tell someone that they're signing up for this amount of work/ cost) - oh and it's not just so that the fish has enough room to swim, if the tank is too small it means that there's not enough oxygen in the water for them and they very easily end up suffocating/ being poisoned by their own waste.
Gold fish especially suffer from this - they have the old 'goldfish in a bowl' stereotype and are told that 'they naturally grow to the size of their environment' when actually the truth is that they are poop machines and need big tanks with strong filtration systems and only their outsides grow to the size of their tanks - their organs keep growing and often this leads to their premature deaths.
Well kept goldfish can live for 80+ years and grow massive (Single tail goldfish, like the kind you win at fairs, are actually very closely related to carp)
Sorry, fish rant :V
It just annoys me that there's so much misinformation, so when I get the chance to talk about it I go overboard hahaha
As for rats - I'm not sure myself, the bits of knowledge that I have are because my friend used to keep rats, so I have heard bits and bobs from him P:
I know they are very intelligent though and can be very rewarding pets to own c:
And I know nothing about hamsters!
I'd recommend doing some research using google and finding the animal specific websites once you're a bit more sure on which you want to have c: