id go with the track machine if your not gonna be on concrete alot... look into bobcat there t320 is a beast in just about anything... what type of skid are you useing now cause there offering verry i repeat VERRRY generous trade in values + government rebates on there new machines.
To DaveVB and digdeep516 I see where you are coming from big time sand paper thank you. On the serious side if a person was to rent or by a CTL just how steep of a grade can they handel straight up and straight down not across the face.
You can run on a 100% slope up and down. Rubber tracks are the way to go if you're doing mostly dirt work. Tracks in sand however will eat the drive sprockets, front and rear idlers, and the embedded driving track lugs away very quickly, long before the rubber wears thin. Figure 400 hours max on a set of sprockets and tracks with mostly sandy soils work.
Tracks can run $3500 a pair and sprockets another $1500, plus installation. If you get a CTL make sure you charge more than for a tired machine to cover the added costs. The track wear in sand costs an average of $12.50 per hour over their lifetime.