If you are sticking with SLRs then go F2a. If you are going to get a rangefinder some day then SL, SL2, or FTn.
If you get the F then go Nikon rangefinder like the S2, S3, or SP. If you want a Leica rangefinder ( e.g.M2, M6) go with either of the SLs.
The OM single digits are almost as strong and fine cameras but not as strong as a F, F2, SL, or SL2. Not a bad third place though.