I would go with the dozer.... proper maintaining and it will last you a long time.
As far as the skid steer goes, from personal experience at work..... if you have anything other than flat ground..... you will become efficient at putting the tracks back on or get tired of doing it and sell it. It doesn't take much on uneven or rocky ground, even turning on big enough stobbs can jump the tracks off. I have a system that I use and can get a track back on in 5-10 minutes depending on how far off it is.... If it's bad and all the way off, you have to jack up the machine, remove the cover and open the valve to let out the grease that adjusts the tension of the tracks. Then get the track back on and then put a tube of grease back in to tighten the track back up. It's a PITA and could take 30 minutes or so depending on how prepared you are for the instance.
Each machine has it's place in work environments.