Honestly, you can start out in so many different directions is crazy. You could go live planted or artificial, and you could also even decide to do a habitat tank, where you duplicate the habitat of certain fish.
Those aren't real big tanks and you don't have too many options when it comes to cichlids, oscars are not one of them. If you want to try cichlids on, I would recommend a pair of Kribensis Pulchers, they are pretty cool little fish, fairly easy on a planted tank, so long as everything is anchored down, and they can be fairly personable.
For the ten, I would more than 100% recommend doing a female betta tank, plant it well, very well, and then put 4-5 female bettas in there, they are sweet, and make a GREAT tank. They have all the personality of males, if not more, and they have stunning color! When you sit down next to the tank, they WILL come over to see what you're doing, or maybe they just want food? I like to think that they want to see me.
Or a little dwarf puffer in the ten gallon! That would be cool! Maybe a pair of Killifish? The tirthy would be nice with a small pleco in it too, maybe tetras, with a really nicely planted tank, black sand, and lots of open swimming room, you'd have a hella active tank.
Maybe a pair of Honuran Red Points in the 30, they're pretty personalble and very pretty when in breeding colors.
I dunno, but I can think of a few others if you'd like!