A few thoughts on my admittedly limited experience with both tiles and stones. I'd go with a good stone if you've got the room in your oven (and the cash). I use unglazed quarry tiles in my convection oven because I haven't been able to find a stone that will fit. I use a stone I got from Baker's Catalog (1/2" I think, the thicker the better) in my gas oven, and that's where I make my pizzas. It does a very good job for me. The tiles do a good job as well, for don't build up the heat mass (in my opinion) offered by the much more substantial stone. I have no experience with FirbraMat.
The tiles are cheap to replace, but may also move around on you and are not of a piece, as is the stone. I have read that some bread bakers go through a lot of stones, and blame it on the frequent spraying they do to achieve a good crust. Besides dropping a stone, I don't really know of any more ways to break one.
I've also discussed cutting my stone down to fit my convection oven with the folks at Baker's Catalog, and they see no reason it shouldn't be done. I am fortunate to have a mason as a neighbor, and his wet saw should do the job.
Final thoughts: if price is a constraint, having unglazed quarry tiles is absolutely worth doing and you can get them for next to nothing ... if you can find them. I had a devil of a time and finally contacted dal tile directly and got great results. I can't see enough good things about daltile. Their local representative (a warehouse) actually gave me the tiles I needed so I wouldn't have to buy a whole case.
The stone I got from Baker's Catalog was around $30, I think, and I've found it be a bargain. There is one more alternative: firebrick. Wood-fired brick pizza and bread ovens use these for their hearths and vaults. I can buy them locally for about 82 cents apiece, and they come in different sizes. If I do cut my stone down to fit my convection oven, I may try firebricks in my gas stove. And I'll probably work up a "stone" to fit over my pizza and bread, probably from daltile unglazed quarry tiles because of the ease in handling, as they'll come in and out. I leave my stone and quarry tiles in my ovens all the time now,unless I'm afraid something greasy, etc. will drip on them. Cheers.