G3 is awesome, works well with 50cc kits, 70cc kits, and stock cylinders.
Leovinci is okay, apparently the muffler is restricted and has a ton of baffles and stuff in it. if anyone get this one, just be aware of it.
if you can mike, see if you can get the doppler in stock because its so well rounded and works so well on 70cc kits and maybe the kenji too. it works well with lower revving motors which makes it great for stock bikes.