Eddie,
If parts are a big concern I would offer the following information. The F series are great tractors and the features are fantastic however certain parts can be tough to get within the normal 3-5 day UPS. For example, I usually go to Anna at Southern Global and Danny at Fredericks Equipment for my Yanmar parts. Between the 2 of them they have everything for every YM series tractor ready to go and usually ship it the next day. Their stocks of parts for F series tractors are a lot less and the FX even fewer. The reason for this is the F-series tractors are much later models and there are tons of YM series here in the states. Most of the YMs were made in the 80s and have been coming over for years. The part yards have a ton of them to even pull the rarer parts.
Ultimately you can find someone with a part for all theses tractors, with money and patience. So the question I would have you consider is how bad would it hurt you if you had to wait on a rare part for 3-4 weeks while it was shipped from Japan? Just to clarify what I mean by rare parts, simple things like starter motors, alternators, ect are readily available for all these tractors. These discussion boards are a great place to find parts suppliers. It is the transmission parts for F series that are harder to come by in my experience. If you use the unit for commercial work then the YM series have a much lower probability of someone having to go overseas to buy a part. If this would not kill you then the answer is the F series are really cool tractors and I love the look of them!
I fully expect that over the next 2 years more F series will come and more the parts suppliers will have more parts and parts tractors on hand. Rare parts really don’t become a too big of an issue if you maintain you tractor and don’t push it past what it was meant to do.
I don’t want to suggest that every YM is easy to find part for by any means, just that they are easier that the Fs. There are within the YM tractors some models that are more popular like the YM 2000 I believe is most common over the last 10 years and you can get any parts anywhere in the country because there are so many of them.
The other advise I would offer is make sure you by an F series from a dealer with a parts guarantee to ensure they are on the hook to support the tractors they sell.
I hope that helps and good luck hunting!
Best Regards!
Bob