Which type of mask is better, a purge valve mask or a non-purge valve mask? Is it a matter of personal preference? What are the pros and cons of each type?
The best mask is the one that fits
you the best, leaks the least and gives you a good field of view. Nearly everybody in this thread has an opinion, and if they say "Don't get X" or "You have to get Y", they're completely irrelevant.
If you get a mask with a purge, you can clear it by blowing air into it. If you get one without a purge, you can clear it by blowing air into it. The only real difference is that the non-purge mask requires that you tilt your head back a little.
If you get a high volume mask, you can clear it by blowing air into it. If you get a Low Volume mask you can clear it by blowing air into it. The highest volume mask I've ever seem could still be easily cleared on much less than one breath. Low volume masks have a little better field of view out the front. High volume masks have side windows for a good clue as to where your buddy is.
The purge valve as "an additional failure point" is a completely bogus argument. They rarely fail and when they do, it just means that your mask now has some water in it. You don't need a mask to breathe. A missing purge valve is an annoyance not a danger.
Buy one that's comfortable, made from tempered glass (side windows, if any, too), has a field of view that you like and leaks the least. If it has a purge, that's fine. If it doesn't that's fine too. Either one will require practice.
You can only find the right one by trying them on personally, preferably in a pool.
Good luck, and don't be discouraged. There are a ton of different mask styles. You might try 20 of them and only find one that you really like. Don't get hung up on what's essentially fake differentiation done exclusively for marketing purposes.
flots.