I had kept my betta for a short time in a 1g bowl, and he hated it. He sulked all day. Now he zooms around the tank all day and comes up to say "Hi!". The 10g is deffinately an improvement.
A 2g is barely enough room for a betta. Endlers and guppies need at least a 5g, and 5 endlers would be the most you could fit in a 5g.GuppyLure, get either 1 female per tank or 3 or more. They'll need to establish a pecking order, and it's too rough on the loser if there's only 2.
I have 1 male in a 5 gallon and he's the most active I've ever seen! But no, I wouldn't say they're as active as guppies or goldfish. For a 2 gallon, I'd say 1 betta OR 2 or 3 male guppies OR 3 to 5 male Endler's livebearers. All of these need heaters. No female guppies or Endlers because you don't have room in there for offspring and guppies can have up to 100 and Endler's up to 40 in each batch! And you could add a snail or shrimp. The Endler's would eat the baby shrimp but not the adults, guessing guppies would, too.