I don't think it's bad to use someone else's engine. That'd be like calling every commercial developer, pussy of the year. A game engine is a way to make a game, as is a graphics API, or a physics system, or whatever. Don't feel discouraged that you're not making your own engine. Besides, making your own engine takes a lot of hard work. It requires tons of your time, as well as a lot of design to get it right. As you can see, if you follow AiGD, the team's been working on this for quite some time.
On the flip side, there's a big difference between an engine API and something like RPG MAKER. From what I can see, you plan to use another engine to program your own games. You're not doing something like dragging objects, and using forms and dialogs to make the objects work. Something Game Maker or RPG Maker XP are famous for. There's nothing wrong with that either, but if you want to make a serious game, those aren't gonna do it (in my opinion anyways).
When it comes to engine's to use, I think I know a few that could be pretty useful if you plan to work in C++:
Irrlicht Engine:
http://irrlicht.sourceforge.net/ - A great engine for 3D stuff, as well as some advanced 2D
Panda3D:
http://www.panda3d.org/ - Nice 3D Engine, I believe there's some Python stuff, but I never bothered to touch that aspect. Plays videos too :D!
Haaf's Game Engine:
http://hge.relishgames.com/ - GREAT 2D stuff; haven't really tried it out too much, but I've heard good things!
Box2D:
http://www.box2d.org/ - Not really an engine, but if you wish to incorporate some physics into the game, use this, as it's the best 2D physics engine I know of. Be warned though: It's a bitch to learn.
I'm sure there's 100's more to choose from, but those are just some that I've either heard good things about/have used in the past. Look around and see what suits you best. Always remember though: "Make games, not engines!"
