I usually keep canned anchovies around, and also like to keep a tin or two of smoked baby clams or smoked oysters. Back in the days of
frozen pizza misery, I'd take a frozen Mystic and just top it with some canned clams or oysters and fresh herbs to get something much more interesting. Now that I'm making my own, I made a couple of pies this past Saturday (which came out superbly, thanks to a thread I now forget that featured a dough stretching video and helped me get thinner pies!). My wife doesn't eat meat, so I made one with smoked oysters.
Now, if I had access to fresh oysters, or clams, I'd use them. But you gotta use what you have. I don't usually keep canned clams that aren't smoked, for whatever reason. I guess if I'm going to make a clam sauce for pasta, I'll get fresh. The smokiness adds a real nice dimension, IMO.
For my wife's pie, I used hand-crushed tomatoes (no sauce), half of a 28-oz. can I drained copiously; 3.75 oz. Crown Prince smoked oysters, drained of oil; 4 oz. Formaggio mozz; 1/2 jarred Goya sweet red pepper, sliced; a sprinkling of a parm/provolone mix over all; and a shake of oregano and garlic salt.
For my own, the only difference was sliced pepperoni for the oysters.
These pies came out closer to 15-16" instead of the former 10-12".
If using fresh, I don't see why you couldn't go with red sauce or white pizza, just like clam sauce for pasta. My instinct would be to go light on the mozz, and maybe go with more parm. Not sure why, just sounds right. I might also add in more allium, sliced or caramelized onions and a bit of fresh garlic. Fresh parsley on top with clams, mmmmm. And black pepper.