I would just say not union... I have had soo much trouble with my contact SLs its not even funny. Even with locktite on the screws i keep having to tighten them, if not my heel cup slides outward and that is not good cause then nothing fits. That was a daily thing for me.
I just picked up some k2 hurrithanes and i can already tell they are better, they just feel waay more solid compared to how cheap unions feel. Thats just my opinion of union. Now that they have this ugly almost non functional toe strap, i wouldn't go anywhere near them.
I also checked out flux in the store and i didn't like the way they felt, very cheap, but the main reason I didn't get them is cause they just didn't fit my boots very well, they have a pretty wide toe area.
Check out Raiden bindings, Rome, and K2. K2 i feel has the best value having their normal 2 strap bindings under $200 but I am slightly biased cause i just bought a pair.
I had some older ride bindings before my unions and I was actually happy with those. but this was before they redesigned their toe strap with the web, which i have heard is one of the best toe straps.