Competition sub are just plain old subs. Its kinda like "Tommy Boy"-I could take a crap in a box and call it gaurenteed, but it would be a garenteed piece of...well you know. So to answer your question, any sub will do, comp or not. You just have to look at the RMS. The higher RMS, usually, the beter. I mean if you want to compete, than you will have to do some custom work. but a good sounding sub is JL, Alpine, or even Rockford Fosgate.
Competition subs are way more than you need. They have pretty much zilch clarity and way more power than you need, besides only coming in 15" and below. The cones are usually cheap paper since they blow them often and need cheap replacements and they arent designed to last very long.
There are so many compitions subs out there ,Pretty well what you want to know first ,Is how much do you want to spend ,and are you going to enter compitions with them.
I would go with the inhumans ,or maybe the power HX2.Do not go with the MTX RFL ,they are not worth the money .They made last for 5 compitions.