well 2 10's should have the most output obviously, most subs you'd be looking at a box around 1-1.5cuft for 2 10's which isn't big at all.
personally I'd choose between elemental designs 11kv2 or 11ov2, image dynamics id10 or idq10s, infinity kappa perfects, alpine type-r's, RE Se, soundsplinter rl-i (tc2),
single 12" setups I'd look at: idmax, adire audio brahma if you can find one, JL w6v2, diamond d9, soundsplinter rl-p (tc9)
the idq's you could save a lot of money on by buying the v2's if you want, which should still be sold new from a few places. the v3 went up in price quite a bit.
brahma I almost bought when I got my idmax but they are power hungry and even harder to find than an idmax. sidenote about idmax is they aren't built to take a lot of abuse, gaps are kept tight to keep efficiency up.
I haven't kept up with ascendant audio but I don't think I'd buy any of their new stuff, I heard a long time ago they ditched their xbl^2 tech, and it might be coincidence but after I heard that I also stopped hearing about AA all together.
RE makes good stuff, I would just never buy it myself because I think they are seriously overpriced ($1500+ for the xxx? please). Still, the SE's aren't too bad in price. Just be wary of their customer service.
I'm sure there's like 20 other brands that have popped up in the last few years that make good stuff too, I just don't know about them.
I'm obviously biased here because I like my idmax, and I was impressed by the 16kv2 I used to have running as a home theater sub. Personally out of curiousity to see how good eD's O line really is I'd probably pick up a pair of 11ov2's. That, or a pair of rl-i's, and after that I'd just stick with my idmax.
Not a lot of help I know lol. There are also solid companies like Memphis that make great speakers but I don't know enough about the brand to speak towards a certain model.
Btw - Assuming your amp puts out 8-900wrms @ 2ohm, I'd just run it at that for whatever it is you end up buying