I've had every type of FF rail system so far, except for LaRue, Troy MRF (on the way, though) and Knight's URX (until it recently became available, it was almost unheard of to see one). Let's see, I've had a YHM, Vulcan, Oly FIRSH, KAC, DD, PRI, POF-USA, Bushmaster B.M.A.S. - same as YHM, RRA - same as YHM and an ARMS SIR (never installed, only owned one and sold it so I won't comment on the application side of it).
Of the inexpensive ones, which would be YHM, Oly FIRSH and Vulcan, my choice would be the Oly FIRSH with YHM a close second. I think the Oly FIRSH installs alot easier and felt more stable to me. Both of the systems will require the FSB to be removed, so that aspect of the systems is a wash.
I had a YHM rail system twist loose on a pretty decent "hit" and I won't own another one again. No matter how tight I made the locknut, even with some Loctite, it still came loose. I'm thinking the Oly FIRSH might do the same, since it is also only held indexed by friction, but mine never did, but it never took the same shock that my YHM rail system did.
The YHM system would be perfect for a casual shooter who is on a budget and wants some rail estate (haha, get it, rail estate) for mounting accessories on. More rigorous shooters may want to consider something with a positive locking system for the rail, like LaRue, which also has a locking system for the rail nut - the best of both worlds. Positive index lock and positive rail nut lock. That will be my next rail system purchase.