I run a top mount on my newage and run pretty big power with no issues. It does really depend what you want from the car. If you like the look of a FM then go that way. If you want the standard look then get a TM. If you want to run big power you need to find a very efficient one though which means more money. Size isn't everything so don't just go out and get the largest you can find. The cheap ones are cheap for a reason, it's all about the core and core flow characteristics. Mine is pretty trick, it's more efficient than a FM, and good for lots more power with less lag than the original STI TM but all that comes at a price.
As I said though its all about what you want to get from the car, what application it will be used for, and what look you want. Oh, and budget.