I've used both systems in my past professional career, finally favouring the Nikon system for the following reasons:
The MD12 motordrive quicker and more straightforward to connect than the Olympus equivalent.
The flimsy cover over the drive connection point of the OM's is easily dislodged and lost.
The FE2's flash sync of 1/250th for all flashes is far superior for fill-in flash than the 1/60th on OM's.
Nikon (in UK) still offer repair service for FE/FM series. Olympus only interested in digital users.
OM4's heavy on battery power. FE's & FE2's battery use much more frugal.
In general terms I found Nikon SLR's stood up to the demands of professonal use with more reliability than the OM's, which needed rather too many trips back to the repair shop, although I realise the OP will not necessarily be putting it to this kind of use.