Considering an OM there are only two decisions to be made:

aperture priority automatic or purely manual
Spot metering or center weighted integral

Spot metering and aperture prio.: OM2 spot, OM4
center weighted integral and aperture prio.: OM2, OM4

Spot metering and purely manual: OM3
center weighted integral and purely manual: OM1, OM3

The purely manual cameras have a mechanical shutter and will work without batteries
Any of the cameras with electronic shutter can be used manual in the same way as the cameras with mechanical shutter.
As far as I know, the OM2spot can not be repaired anymore
The OM3 can be hard to find and is expensive. An OM1 is dirt cheap. Though the OM1n has some internal improvements over the OM1 I see no reason not to try an OM1 if you do not need a motor drive or the flash ready light. Someone has said that something is perfect, if you can not leave anything out without making it worse. To me, in this regard an OM1 is just perfect.
A CLA (and battery conversion) is not part of the decision process as any one will need it as long as the seller doesn't tell you the camera already had one.