You basically asked I want a car but I don't know what type I want.
Mausers come in all sorts of variety, there is likely one in pretty much every caliber made, and pretty much any configuration. There is carbines, short rifles, long rifle, high end, and low end rifles. There are sporters, in a variety of different types from factory made, to custom gunsmithed, to bubba with a hack saw. There is crude (like the Late War K98ks) and there is extremely fine (pre-war Commercial Mausers).
It depends on what you are looking for. Do you want a hunting rifle? Do you want a collectors piece? Do you want a shooter?
If your goal is beautifully made and finished rifles, look at Brazilian Mausers, or Argentinan Mausers (there is a beautiful M1909 Argentine Mauser on the EE right now) as a example of what can be found.
Things to consider is the older the Mauser the farther the minimum sight setting, most start at about 300m. Bent or Straight bolt is a personal preference thing. Other than overall condition look for if the serial numbers match, most Mauser manufacturers stamped pretty much every part with a serial number.
In terms of caliber, I will give a quick list of some you might encounter. 7x57, 6.5x55, 6.5x57, 8x57, 7.65x53, 30-06, etc. Basically do your research in terms of caliber, but most are easy enough to reload for once you have the dies (for example 7x57, 7.65x53, 8x57, and 30-06 all use the same case head, and can all be made from cut down .30-06 or just buy the brass from the store).
I would recommend buying the book 'Mauser Military Rifles of the World' by Robert Ball. It gives a very good general look at Mausers, covering them by country generally with pictures of each specific rifle. At the bare minimum it can help you in the future if you ever need to identify a Mauser.
