If you are new to surfing and shortboarding specifically, I would not got with anything but a thruster. There's a reason why most people ride them.
i got a thruster first before my retros, believe me i love the retros much better (im a fish fan) but the transition from the thruster to a retro will be a lot easier than a funboard to a retro..
i use my quad most of the time but when its bigger i still bring the thruster out. pumpmaster makes a good point, also once you find out what shortboard you should be riding its a lot easier to figure out the sizes of your specialty boards
I guess I'm biased because I rode all those types back in the old days before they were retros and hated them. All my non-thruster types ( a twin and a quad) all have modern templates. Don't get me wrong, those types of boards can be fun, but for a solid, ride in any condition board for our area, I just don't think you can beat a thruster.
True for all out performance go for the shortboard, but since the op says he is riding a fun shape the next learning board would be a fish. its looser then the funshape, but still paddles well.
i went from a 7'4 funshape to a 6'3 performance thurster. i hated the thruster because it was just to loose and i didnt know how to ride it properly. traded up and got a 6'4 fish and couldnt be happier.(except for days where its Overhead+ then i wish i had a board i could duck dive.) surfing my quad fish has made me a better surfer over all, teaching how to keep speed and turning to stay with the wave. once you get those under control then move to a thruster. but go with the fish to get better
gotta tell ya... I'm gald I brought this to you guys on here. Getting everyone's opinion has really helped out alot. I still didn't decide what to do yet but all very good suggestions and appreciated very much