This is my opinion on a few masks that has already been stated here, I do own these masks and speak from personal experience:
Dye i4 : Recommended for the smaller faced players and those who like to have an overall smaller profile. I have a pretty long face so my chin kinda sticks out whenever I shout. Minor thing but it does bother some people. The i4 mask is sleek looks hell sexy and it works fine for those who wears glasses too. I have a friend who wears those thick flat black plastic glasses and it fits in pretty well with his i4s, no problems whatsoever. Visibility wise I would say one of the best out there, the lens is pretty wide which i really like. Lens changing is very easy, not as simple as the e-vents but still very very simple. I havent had a bounce off the mask so far mainly because it is fairly difficult to skim across as the profile is pretty darn small in the first place. One thing i dislike about it is the breathability, it doesnt have as much air holes as other masks, some might find this a problem and some wont, but personally i like masks which give more ventilation as i tend to run outta air after running and diving for a period of time. If your outta shape and gasping for air, the last thing u want to have around your face is an i4. One word of advise is to try on the mask first. Some ppl really dislike the size of the i4s, but if u have a small face/head then it should be fine.
JT proflex : Might say its my favourite as I do use them more than any of my other masks. The first thing that i'll say is that the breathability of this mask is fantastic and you wont have any problems hearing or communicating with your teammates. It is definitely bigger than most masks out there (i.e. bigger profile) but the probability of getting a bounce kinda compensates for that fact. They do call it "pro-flex" for a reason, the mask is very rubbery and soft, you wont believe it till you actually come across one and touch it. That's the mechanism of how it allows bounces. Very comfortable to wear, not as snug as an i4 but feels very light. Vision is good, soft ears do get bounces from time to time as well. The main thing I like about this mask is that the customisability is endless, you can change the lens/eye frames/face plate/soft ears/straps to your liking and well practically you can just have one mask for any team color you play on, you'll just need to customize the colors with parts and you're off. The one thing i dislike is that the lens changing is kinda difficult. The first time I tried to changed the lens I managed to accidently snap the one I was trying to take off, it'll take at least one time to get used to changing the straps as well. Another thing is that I found the bottom part of my faceplate kinda gets in the way when I bring my marker up to aim. I hold the marker in a more elevated way and maybe thats why its like that but during breakouts when I lift my marker up to aim and a speed the tank kinda hits the bottom part of the flex and pushes it upwards a bit which i find a bit dangerous at times.
Empire E-vents : I would say its a bit of a mixture between both the i4 and proflex. It isnt as small profile as the i4s but certainly not as big as well. It wraps around the face pretty nicely with a snug fit. Lenses are pretty wide, visibility great. The lens changing on the e-vents in my opinion is the easiest out of all, even a monkey can do it. Breathability is fine, a satisfying amount of airholes. The materail used to make the mask is pretty flexible as well, i've had a couple of bounces off it. Not much to say about the mask though, it is a great mask just that it probably doesnt look as cool as an i4 or as customizable as a flex to most people.
V-force Grillz : The first mask I ever got. Looks nice, kinda makes you look like a pissed off duck. Vision is great and the lenses are not too hard to switch out. A good amount of airholes for ventilation. I would recommend wearing a headband if you decide to get this though as without the visor it does leave a slight "U" curve exposing the forehead. A ball straight to that spot and you'll have your friends and family laugh at you for a week. The foam positioning is also one of the best, you wont have like some of the foam bunching up in different areas of the frame. However, it did fog on me once for some reason and I think that was when I played for the 2nd time with it on. It does have an average profile to it, not too big not too small. One thing I like about it is that it fully covers my ears when and its surroundings when I wear them, I wouldnt have to worry about the insane pain if I get copped around that area.
Proto Switch : Bought this mask just for fun and gave it to my cousin. The price of it is definitely cheaper than all of the masks stated above, but the material its made of is pretty hard and it would definitely not allow a bounce. It does have a snug fit but then again its more for people with smaller faces that would find the full benefits of the mask. Vision is fine and breathability is ok as well. However, if you're gonna play paintball regularly I would suggest the previous stated masks instead. They are pricey but in paintball you really do get what you paid for.
Rage Headshield : In my opinion, forget about it.
p/s dont worry about getting hit behind the head dude. It only happens from time to time when someone bunkers you and even if they did most of the time it would be the side of your head at most. If you're considering scenario wise, the only reason you'll ever get a hit behind your head is if you turn your back and run away from the enemy in plain sight or someone in your team decides to let the enemy pass through your line and backstab or well friendly fire. =)
Hope you find this useful mate.