Personally I'd go eheim, I've used a few eheims and highly recommend them and with german build quality you are guaranteed a reliable, long lasting filter. But I'd go with the 2215+ or the 2217+ rather than the 2213, better filtration and also have the option of using them on a larger tank should you ever upgrade. I currently run a 2217+ on my 33 gal tank.
I'd rule out the fluval 205, have a bit of a reputation for leaking, think its a bit of an intermittent problem but they dont seem to have the same good reputation as the fluval internal filters have.
I've heard a lot of good things about tetratecs although never used one myself.
I guess it comes down to price, if the tetratec is well cheaper then go with that but if its around the same price as eheim then I'd go eheim all the way. I got my 2217+ complete with hoses, taps and sponge media for about £80
Andy