Hi chain.
We are proud owners of a 289D, and less proud owners of a New Holland C238.
First I'll talk about the cat.
This is our third Cat skid loader. All we've ever done to them is check the fluids, grease them, and go to work. They have spent most of their lives in the dirt, are put in the shop during the winter when not in use, and have made us a nice bit of $$$. We baby them, and they in turn hold their value. We had a hydraulic hose on our 279C get a hole rubbed in it towards the thousand-hour mark, but other than that no issues. All in all they have been great machines for what we use them for. I really really like the backup camera. Highly recommend if you go caterpillar. Not sure if it is an option on terex/NH
Our New Holland is a "ranch machine" - by that I mean it stays out at our ranch and gets all of the **** jobs, such as literally anything to do with trees. It is our second New Holland. The first one was a bit of a melon, front idler went out on it fairly early in its life. I attributed this to the heavy tree shear it often had mounted to it. In my opinion counter-weights would have helped. Not too long ago we traded it for the New Holland we have now. I have not ran it much but I haven't heard of them having any issues with it, no news is good news.
I know a guy who runs a Terex forestry unit. Looks like it is a mean machine set up for really ****ing **** up. I personally don't buy into all that extra protection crap, I like to think I would be careful enough with my machine to not need that protection, but it takes all kinds. I think he has pretty good luck with it. He has a big rotary grinder kind of a deal that pulverizes trees to nothing.
It sounds like you're going to buy a brand new machine, so I don't know what to tell you. I've never priced the terex, the Cat will be at least $75k, and the new holland was cheaper than the Cat. Go sit in them all. See what the visibility is like out of them, climb in and out, switch attachments, etc. I will say the multi terrain loaders do have a smoother ride than the compact track models such as your 299D. Considering how much you will be traveling around after trees, definitely something to consider. Also, on side slopes, the multi terrains (277,287,297 series) have less of a tendency to slip a track. While simply keeping them tight eliminates the problem for the most part, again - something to consider.
Putting a skid in the trees is a catch 22 in a lot of ways. It's going to be hard on it. You're probably going to **** some **** up. I put those tree attachments on the same level as a concrete hammer on an excavator. If you need to do it for awhile, fine, but don't tell the guy you sell it to you had one on it. Since you're buying new and not trying to buy an undersized machine for the attachment you are wanting to put on, you shouldn't have any problems with whatever direction you want to go. Run it until it hits 1000 hours and trade that son of a bitch.
:my2c