I just broke another guitar string while tuning. I realize there are many different types of strings to choose from and for this reason wished to ask: which type of steel strings for an acoustic guitar is most durable?
Lots of factors can lead to string breakage. As a general rule of thumb, lighter-gauge strings are easier to break than heavier-gauge strings. For a beginner, on an acoustic guitar (as indicated in the comments) .012s or .013s should not cause any problems; I wouldn't worry about fancy coatings or string alloys with respect to string breakage (these features might make strings sound alive longer or otherwise change the sound in a way that you like).
There may be rough patches on a fret, or rough edges on a saddle that lead to more breakages than usual. In the first case, the string will probably break somewhere in the middle, and in the second case it will probably break at the saddle. If either of these is the issue, you should probably take the guitar to a tech for a check-up.
String installation error is a common cause of string breakages. It is relatively easy to get a kink in a string during installation: you can pull a looped string and inadvertently kink it when the loop tightens; you can begin to tighten a string, realize that you need more slack, loosen and re-tighten to find a kink where the string had passed through the post; sometimes the ball-end of a string doesn't seat quite right at first and slips during tightening to reveal a kink where the string passed over a saddle. Kinks like this don't always seem to cause a problem once the string is tightened, but certainly can lead to a weakening of the string and eventual breakage at the point of the kink.
The most common installation issue seems to be a failure to get a clean wrap at the post. You must have enough slack in the string to get a few neat wraps around the post when the string is tightened (two or three wraps should suffice). The string should not cross over itself as it wraps the post, and it should move down the post as it is tightened, with the windings sitting snugly next to each other. It is very common for string breakages to occur at the post hole when there aren't enough wraps, where the edge of the post hole applies too much stress on the string; the same thing can happen when string windings cross over each other, generating too much stress at a crossing point. There is also a way of tying the strings to the string post that involves some string crossing, but that is a different beast; it is a little tricky to implement and not really necessary, so I won't go into that here.