As others have said the end result will depend on what is right for you as far as the controls, etc are concerned.
That said, as a mechanic who works on all brands, I'll give my input on them in that regard. I work on alot of the older Bobcats like the 743, 753, 853, etc, and have also done some work on the tracked models like the T190 and T250's. Like any of them the wheeled and the tracked ones can be a PITA because of space considerations, but on the mnajority of them the cab raises right up to make working on them alot easier. The main thing is they are extreemly common, and easy to get parts and information on. Like any of them the electronics are prone to having problms, and when they do you either have to find someone with the computer to work on them (something I don't have myself) or take them to the dealership. One problem I have seen there is the linear actuators that control the hydraulics going bad. When they do they are expensive to replace. That being the case your best bet is to find an older one that either has no electronics at all, or a newer one that has nothing but the black box safety system (BICS) system on it. Those are't that hard to work on and aren't all that problematic when they do mess up. Plus you can usually get a new black box for around $250 is problems do arise with it.
As far as the Deere's go working on the ones I have was a royal PITA. I say this because to tilt the cab means the boom and bucket all tilt with it. As a result you can't do it by hand like a Bobcat, so it takes a special tool from Deere (which was extreemly pricy when I checked a year or so back) to jack it up and hold it in place....or you pick and hold it with a crane, like I did. Once up though it opens things up and it wasn't that hard to work on. As far as parts go, at least as far as the ones I had to get, the weren't unreasonablely priced and were pretty much on par with everyone else for similar items.
As far as Gehl, I've got one setting outside now with the drive motor out of one side. On this particular one the drive motor's main shaft and the chain sprocket are all one piece. What this means is that when something happens to the motor, the sprocket gets worn, etc, the motor has to be rebuild and/or replaced. The one I'm working on has been sitting for over year now because the rebuild cost on the one drive motor was going to be well over $3000 because that main shaft was going to have to be replaced, and my customer hasn't got that much money to spend on ir right now. Beyond that design wise the ca tilts alone making working on it relatively easy.
As far as the CAT's go manuals for them are going to be through the roof. Looked into getting a service manual for one a few years back and the cost on it was around $1100. That said CAT's entries into the market all have more than their fair share of electronics on them, and being a CAT, part's aren't going to be cheap. Not to mention you just about have to have the service manual to do anything but the most basic repairs on them because nearly every sensor, etc feeds back into a computer which in turn tells everything else what to do.
Just had a LS180 nw Holland leave here this morning I had done some minor stuff to. Like any of them the electronic parts are PITA, but accessibility to work on them, etc was pretty good. Parts are a crap shoot. By that I mean an alternator bracket for this one wasn't but $11 but the wear strip for the side of the cab was nearly $43.
As far as accessibility goes I worked on I believe it was a Komatsu a few years back where the cab tilted Forward. This opened up everything and made working on it a dream as compared to many of the others. Beyond that my experience with them is limited other than to say Komatsu parts for other machines I routinely work on aren't any worse off price wise than any of the other brands. In the end I know my customers have Bobcat, and New Holland skid steers more so than any of the other brands. The one thing I have heard about them is that the newer ones with the higher, cab forward design do give a better sight picture to the bucket edge if that matters to you. While I can see the advantages of something like that in certain instances, the way I look at it is operators were doing the same work with the older machines as they are with the newer ones, long before the newer ones were even though of. In other words sight lines to the edge are nice, but in the end it's the skill of the operator that is going to make the difference.