I'd go for the 6 burners myself; I deliberated long and hard on this when we were looking at Bluestar ranges, and what made sense to me was that 6 rings all the time are more useful than 4 rings and one only-griddle. You can buy a good cast iron or stainless griddle that's easy to remove to wash for under $50, iirc.

Initially I LOVED the idea of a permanent griddle (shrimp!), or a French ring (sliding big pots of good food around!), but eventually I'd have gone with 6 regular burners because that's obviously the most versatile option...........and then we got lucky and found a vintage Aga, so that was the end of my Bluestar dreams. :)

Which cook-top are you looking at? Bluestar were absolutely super to deal with, and I LOVE that they're no-nonsense commercial stoves, vs domestic stuff (Wolf, Viking) pretending to be commercial, available in a gazillion great colors which I can play with online ad nauseam:
http://www.bluestarcooking.com/build-your-bluestar

If we'd had space for the 48" then we would probably have got the 12" char broiler, but even with just the 6 rings we'd have needed a substantial range hood and make-up air, and in our climate - cold Ontario, Canada - that would have been daft. No exhaust needed with my Aga, thank goodness!

The other brand I liked was Capital Culinarian.

A non-built in griddle can be easily changed if it's damaged, otherwise you have to special order a new one, which in the future may be a discontinued item