I throw both, though I would say that the Sidewinder is the more verstile out of the 2.
I use the RoadRunner for right turning shots, tunnel shots, and rollers only. I can put lots of hyzer on the disc and it still turns, so I keep in mind how far or how much I want the disc to turn and adjust the hyzer accordingly.
The Sidewinder I throw can be used for tunnel shots, right turning shots, and rollers as well, though it can also hold a long soft hyzer and can also be flip hyzered to str8-as-an-arrow flight.....I took the thing out of my bag, along with a Beast, because of really used Champion Valkyrie.
Sidewinder is my vote. It's the more versitile disc.
If you're having problems getting the RoadRunner to stay in the air (my guess is, is that it's rolling out on you) put more hyzer on the disc when you shoot and maybe throw the disc higher in the air.
If you flip hyzer the disc into it's turn, you'll generally get a lift early in it's flight to help it get higher in the air, but the flip hyzer also uses the discs SUPER understableness to turn 'up' into the air instead of the disc being thrown flat and it's SUPER unerstableness turning you into the ground.