I vote for a track loader-as in hi-lift- not a ctl. There is nothing more versatile than a track loader especially when talking about hydro machines. You will be able to hog dirt out instead of having to load and haul with an excavator. Either get an older clutch/brake machine(not a 939) or spend a little more money and get a 943 or 953. I personally like the B series over the C series for simplicity and ease of service.
The other buy option would be a D5 or D6 B-D series. Picking up some implements can increase the use of your dozer. A dolly scraper and disk are will add to your capabilities if you want to pick up work. It will be hard to find any machines in true working condition for ~10K. Your either gonna have to be patient or willing to work on your machine. 15-18K will get you a better machine a lot quicker and if you don't know much about these machines find somebody who does.
If i was gonna rent a machine i would go with a D6 hitrak with s-blade and slot push the pond out. No ridiculous rent, fuel or mob costs, but will still work fast enough to keep the number of days of rent down.