Definitely multi mains and poly crosses.
This setup gives a better feel and a little more power.
In terms of spin, it seemed to me that I was actually getting more spin with a full bed of poly, but the hybrid setup feels a lot better and gives me more power.
As for tension, It depends on what combination of power/spin/comfort/control you want.
From what I've seen posted on these forums, most pros string crosses at 2-3lb less than the mains. I tried the same thing, and it works well. I guess this allows the mains to slide more easily over the crosses, and produces more spin.
Wilson BLX ProStaff 90: 368g, 7pHL, SW=352. (Wilson NXT 49lb / Lux AluPower 45lb).