273 Y-pipe?

Ok, how many y-pipe designs are out there? I found a older tread here that showed a complete NOS commando exhaust and the Y-pipe is a 2 into 1 design. Accurate LTD has an "improved" design and then the exhaust I pulled off my Commando has a "T" design. Sorry no picture, but the drivers side pipe t's into the main pipe.

Are both designs correct? Which one is better in a 2" pipe? Are there other designs as well?