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My repair guy said that the CF is generally more reliable and he has seen quite a bit of my CFi (lol). That said I have both and use the CFi daily as its a smidgen sharper of the two with my P-45 digital back but the CF comes out with us as backup. We shoot most days and the 100mm is the main lens used so it does get a lot of use.
If you are shooting film go for the CF.
I'm intrigued with the 100mm as it has such a great reputation and have looked a few times on eBay. Whilst the CFi is expensive, it's nothing like the price of a 110mm FE AND a 203FE body to support it. The 110mm is unique in the whole of MF, but it's use is limited to the 200 series cameras and I'd like more flexibility which I'd get with the 100mm.
Why is the CFi "unnecessary" for film and the CF OK ? I tend to buy best in kind, but that's an expensive habit.
If the "i" is the sign for an improved internal coating to reduce lens blurr through internal reflections, it could be possible that you can see the difference more in digital sensors , because the need the light hitting the sensor plane in a more demanding angle than film emulsion. All kind of stray light will make this worse.
I know that Zeiss used to have in some lenses up to 7 different paintings internally to avoid reflections within a lens.
You could see this differences also in comparison shots of the Zeiss Touit 32/1.8 for Fuji X vs. the Fuji XF 35/1.4. The Zeiss was significantly better in reducing this flare.