qph031 is the best out there for getting both dbs and ku.... but, as mentioned it's big and slightly heavy (has 4 lines out, two linear and 2 circular)... I too had problems with it falling off the arc due to the heavyness, but after doing a weekend or two of playing with the dish, got that issue fixed good by sturdying the dishes mount a lot more than is probably necessary. I have one of Sadoun's roof mounts (the one that's suppossed to always end up being plumb), but it kept falling off of plumb slightly due to weight of the lnb/sg2100, etc. I put a couple of screws in the roof and used some copper wire, tied wire to the screws and the other end to the pole. After a while, got it nice and as plumb as plumb can be. Since it's copper, it's starting to rust a bit, so I'll probably get out there someday and put some electric tape around the wires to make it less rust-prone and/or use some new wire of some sort that's less rust prone.
Also, to keep lnb itself from falling, I have some wadded up electrical tape under it, and that's taped up to the arm. May look bad, but I'm tracking the arc better than ever nowadays.
qph031 is nice, just know that before you buy it that on a smaller dish, you will need to rig up the dish to be a little sturdier than as if you put it up with no extra support.