get a Vanguard Demon and get it working.
build a Shocker.
chop up a Tippmann.
create a Spimmy.
scratch build a sheridan or nelson.
buy a Merlin extrusion and have some fun building it into whatever you can think of.
think about what you like and what you want and go for it. i like ICD, so i would go more towards that, but your question is ambiguous and open ended, that a proper answer is impossible.