I switch it up but front crawl (free style) is what I spend my most time with. I also do a fair amount of butterfly but I wouldn't recommend off the bat, you have to develop some upper body strength and a fair amount of breath control to not drink half the pool. Breast stroke is nice smooth motion that lets you bring your head entirely out of the water, I have to dolphin kick instead of frog kick when I do it cause I can't get my hip to turn the right way but it still works just fine. Backstroke of course keeps your face out of the water the whole time, I've really never like it though cause I hate not being able to see where I'm going and it also doesn't feel like as much of a workout unless I'm really going for speed. Another thing that might help is kick boards, (hard normally blue foam half surf board looking things) most pools that are set up for lap swim will have them, you can use them to just practice kicking keeping your head out of the water which is still a hell of a work out. There's probably some good videos out there on breathing techniques, I don't think trying to describe them in a written message would help that much.