what are the pros and cons of having a returnless fuel system?

 

con, putting extra fuel into the engine is a hard process

 

Pro's: lower emissions
simplicity and fewer parts

Cons: can't use a fuel pressure regulator to add fuel for hi powered forced induction setups
limited choice of hi flow fuel pumps

One is not better than the other, but return systems can be easier to tune if you're on a budget. Returnless systems usually require going the more expensive route of larger injectors and ecu trickery (or a standalone ecm).