How Can I Paint a Popcorn Ceiling?
Get a large napped roller, 3/4 inch, a 5 gallon bucket and a bucket screen for the roller (don't use the little trays), a wooden rolling pole can be purchased cheep. I would also get a spray soc or where a cap when rolling ceilings. You will get a little of the texture in the roller, as long as it is not a large noticable amount, then it should be ok.
What type of spray rig do you have, airless, cup gun, pressure rig?
If you follow Chip's advice (above), you'll probably have no trouble. Make sure the paint is thin, not thick and sticky - even if it means doing extra coats.
The best way and to most painters, the only way, is to spray it, hands down.