Mylar is much more reflective, I don't know how and why people are having problems installing it. Having troubles doing a two man job by yourself shouldn't warrant a "zomg too hard". Just get someone to help you. Find some cardboard, then cut 1x1 inch squares, use thumb tacks, have a friend hold it, pull it tight and tada, wrinkle free.
Although white paint has way more pros than cons.
Paint Pros:
Easy to clean the walls once painted.
Cheap
Easy to apply
Mylar pros:
Can remove it
Much more reflective
It appears that a lot of people on this forum use the actual size of the grow room to determine if they use mylar or white paint. If the room is a huge 10x10 then paint would be much more efficient and easier. But for smaller closets, grow boxes,etc mylar.
Keep in mind if you're covering a small area, there's a fuck ton of it on a roll, so once you get a roll you'll be able to have enough for several times. It basically all depends if you want to spend the extra money, and have a bit more hassles for 10% more light reflection. Also, the good quality mylar is much thicker and slightly easier to work with and it doesn't tear as long as you do the tiny squares of cardboard and thumbtack trick.