I think that the first thing you should figure out is what kind of results you are looking for. Each laser or device is a tool that has specific uses and limitations. The best way to make sure that you are using the appropriate technology is to first define what kinds of changes you want to see - what do you mean by "resurfacing?"
If you're in your 30s and you're just talking about brown spots from sun damage, then IPL may be your best bet. There is little to no downtime and it fades these spots well. I recommend IPL to patients who do not want to incur major downtime and who do not have issues with fine lines, large pores or acne scars. It is cheap and easy, although you do usually have to do multiple treatments. One piece of advice about IPL - don't think that packages of 5 treatments are absolutely necessary. I offer packages but usually tell people that less treatments may work well - nothing wrong with playing it by ear.
If by resurfacing you mean fine lines, enlarged pores as well as brown spots, then more invasive laser treament would be appropriate. The fractionated CO2 lasers are all the rage now and they really do represent an important advance in our ability to correct fine lines, pores and what i call the "topography" of the skin. I use the Active Fx / Deep Fx with good results - the laser has been around for a couple of years and is safe and effective. The downtime is significant - 4 days at home and then about a week where you look like you have a sunburn - but nothing like the pain, redness and swelling of operative CO2 laser resurfacing (which is falling out of favor as these fractionated devices become more popular). I notice that the fractionated CO2 is especially good for lines around the eyes and lips - areas where no other laser seems to make much of a difference. The other advantage of the CO2 devices is that less treatments are needed. Generally one to two sessions are sufficient, as opposed to the 5 or more sessions with the traditional Erbium Fraxel laser.
Acne scars are tough to get rid of. I use the Deep Fx and the results are quite good, but 2 sessions are almost always necessary and there is a bit more downtime. The laser companies say that there is collagen stimulation benefit from the CO2 laser which will improve results over the 6 months after treatment. I'm not sure if that's true or not, but we'll see.
Differences between the CO2 devices are minor, but not insignificant. The Mixto is an Italian device - it is not as versatile or as well supported as the American Active Fx and Fraxel re:pair. It's alot cheaper (for the doctor), but I think that it is not as reliable and cannot treat the variety of skin types and conditions that the other two treat. The Fraxel and the Active Fx are equally good and get similar results.Both devices have more depth of penetration and density than any patient needs - I would never max out either device in the clinic - so this is really not a differentiating factor. I got the Active Fx because it has been out on the market for several years and its safety record is good. The Fraxel is a new device that has also been seen to be quite safe since its release over the last few months, but it is still new.
If you're going to go for one of the CO2 lasers, make sure that the doctor has had plenty of experience and that he or she is either closely involved with the treatment or actually performing the procedure.