Pagestream and ImageFX are definately being done for A1, those plus Papyrus Office for MOS too (these three plus basic Internet is what I need to replace my PC). It looks like any of the big (for Amiga) players are doing OS4 and MOS versions of stuff so far, and will see what sells more to decide future development.
The Peg comes with Linux and MOL chucked in too, though that doesn't really matter to me personally. From what people have said the Peg is very good with Linux, and runs about a half-dozen different flavours without problems.
With OS4 yet to be finished it's too early to tell which will be the best rounded system, I'll just be going to Peg as it's got/getting everything I want (which isn't much ;-)).