Having done both BAC and the VTARNG Mountain Warfare School as a cadet, I'd recommend going either the MWS route or see about getting a Sapper School slot.
MWS is (or at least was...its been a while) a very professionally run school teaching an interesting subject--the military application of rock climbing and alpine operations. You'll also set yourself up to get through the lower mountaineering portion of Ranger School fairly easily.
Short of attending Ranger School, the Sapper Course may be the closest you'll get to working small unit tactics in a demanding environment as a cadet. It would serve as a decent taste of what to expect at RS (patrolling, OPORDS, SUT, etc.), plus you get to do target analysis and make things go boom. Oh yeah, you also might earn the coveted Sapper Tab.
If you end up commissioning infantry, you'll get a BAC slot either before or after IOBC, so you might as well try to broaden your training now while you have some unique options (and some choice) available.
BTW, USMA cadets haven't been able to attend Ranger School since 1991.