I guess we can worry about tractors for longeveity as for most people here at 50 to 100 hours a year that would mean some are built for 100 years for the hours we have seen put on them. So for the most part we should make sure that when you buy the tractor should get the job done for you in a way that you can get your work done in the least costly and convienent way. After all, there are no gaurentee in life but three things.
So look at the operator compartment and make sure it might fit you well, with the fact of the usable life of the tractor you should make sure that the controls you need the most aren't mounted behind you! You should make sure that you have a nice level deck with no levers hanging out to later catch your pant cuffs so when your getting off, you don't land on your face!
The internet has made ordering parts or just getting information on how to fix your tractor easy if you are so inclined. You can see here that it happens daily! Do make sure that the tractor can handle the job well, we often see different makes with bent steering linkages from being in front of the axle and below it from being in mud in the woods and catching a stump or rock. We also see that tractors that turn tighter often are found not to need the brakes to turn! The other thing with this is for those that feel compelled to use the brakes the front hubs and wheels only seem to break from to heavy of loaders and hitting objects and it is rare that they break under warrantee!
Do make sure that you order it with the attachments that you need, within two models you won't be able to buy them other then through parts, and we all know about parts prices!
As far as reliability, I've seen people that keep buying different makes that I thought they had bad luck with as far as the number of times they are down. They felt fine as long as they could get the parts they needed when they were down even if it was often! There are brands out there that are proven, and there are some to yet prove themselves! The market will still change and there is always someone new as well as somethings that are old and still going on.
One thing I've seen is some have the determination to build a better product and some just run off the cuff's of others. Those with the desire to build the best normally do and those that desire to just build for market share put more money into advertising then the product. For some on sales just pick up qwhat they might call their largest advantage, it might really be a fault, that is why nobody else is doing it! They all go on till profit or desire goes away. After all the original S&P 500 only has 13 original companies still there!!!!