Mohunter, I've seen some good advice from the folks here, but really, you need to sit down and take stock of your personal situation.
a) How big an area are you mowing? and how often?
b) How long can you afford to take mowing it?
c) Is the terrain fairly free of obstacles or not?
d) Is the terrain pool-table flat or does it look like someone threw the ground over the billiard balls?
e) How long and what type of driveway do you want to clear?
f) What is your honest assessment of your mechanical abilities? Do you know the difference between a flat-head and a Phillips screwdriver, or is your skill level such that you can take a chunk of steel and bore, hone port and polish your own engine block and build a tractor frame around it?
g) Do you love the control a manual transmission give you, or would you rather use an automatic transmission when you drive a car? (For choosing between a gear drive and a hydro style tractor).
h) Do you think you might start doing chores beyond mowing and snow-plowing?