There are a couple of areas where an Olympus OM4-Ti (or OM-3Ti) are simply unbeaten - in absolute terms - compared to other 35mm SLRs:
- Viewfinder size and brightness, especially with the 2-series Lumi-Micron Matte focusing screens. It's unbelievable, the view is literally as bright and crisp as seen by the naked eye, and better even than the best glass rangefinder viewfinders (e.g. Leica M3)
- Ergonomics: Ability to operate by feel, because of co-axial shutter speed, focus and aperture controls all focused around the lens axis, operated by the left hand. No other SLR can be operated "by feel" like an OM, period.
- Physical size and weight: These bodies are TINY, but very robust (see OM-4Ti crash test). Not Nikon F robust, but among the most robust electronic film SLRs you'll encounter.
The interesting thing is, these attributes don't necessarily make them "better" unless you really value them. For example, I spend as much time with my plain-prism Nikon F these days than what I do with my OM-3Ti. There is absolutely no question about it that the Nikon F, or the early (metal scalloped focus ring) Nikkor lenses are built to a much higher standard than the Olympus gear. Old Nikkors are built to the highest mechanical standards ever achieved by anybody (including Leica) as far as I am concerned.
Want a simple test? Squeeze your Olympus Zuiko lens really hard between your fingers while focusing - you'll feel increased resistance or possibly be unable to focus at all. Squeeze a 1960s Nikkor 50mm f/2.0 for all it's worth (this was one of their cheapest lenses) and the focus is still smoother and better dampened than even new Zeiss ZF lenses, which feel like giant off-brand 1970s cheapies by comparison.
Is this important? Probably not - the Zuikos are lighter, and very often optically better, than their Nikkor counterparts. The marvelous Zuiko 21mm f/2.0 is as small as a Nikon 50mm f/2.0! However, my 50-year-old, never-serviced Nikon F leaves me with no doubt that it'll be working in another 50 years' time (when it's a 100 years old). Not so for the Olympus / Zuiko equipment I have, which are all in various states of operational smoothness, etc. But the Nikon equipment weighs a ton, and is much more primitive. I am certainly extremely happy in using both the ultimate finesse that the SLR world has ever achieved (OM-3Ti, OM-4Ti, Zuikos) and the ultimate unbreakable, simple SLR (Nikon F). I am hard pressed to pick just one.
I am comparing to Nikon's ultimate SLR here - the F - and not a more budget-oriented SLR like the FE series (because I use an F, and have only held an FE2 once). I like not being distracted by silly light meters these days, which is why the F appealed to me. Compared to an FE(2), I would probably choose the OM-4Ti every day. The lenses focusing the "wrong" way will get to you though!
(Nikon's way is "wrong", of course, and not Olympus' - older or not!)