I have painted two garage floors with good experience both times. First floor was about 20 years old and dirty. I used diluted muriatic acid to etch the concrete. This cleaned it well and roughed it, grease and oil spots took a little extra scrubbing. Make sure when you squeegee acid solution down driveway it is diluted more with water from a hose or you will etch the driveway. I let it dry a couple days and painted with Lowe's brand two part epoxy. With the etched floor first coat really soaked into concrete, so I ended up using twice as much paint as I initially thought. I mixed sand in with the paint for traction, sand would quickly settle to the bottom of the roller tray, so kind of difficult to keep mixed up. Sand help a lot with traction. After this dried I put a clear coat on. Clear coat was nice because it would wear and scratch and the color below would not. Then re-apply clearcoat as needed. Moved out of this after 5 years and 99% of the paint was still on the floor looking good.

Second house was new construction, so floor was clean, no oil or grease. I used Sherwin Williams one part paint or epoxy. Coverage was very good. Also used Sherwin Williams clear coat. No sand but did use the flakes that comes with the kit. Year later looks great, 100% of paint is still on floor.

Preparation is the key, especially on older floor. Good luck!!

we bought a 4 yr old home this past October and had the garage floors painted with epoxy paint--the kit where you can add the reflective particles at the end (which we did not do)
our painting contractor did the job--they pressure washed then acid washed the garage floors to rid them of any grease/dirt and to open the pores of the concrete to accept the paint
we used a beige color--the other was gray I think--and I think they got the kits at their paint store or Lowes--forget--
the contractor was pretty open about the reliability of the finish--told my husband that doing it in cold weather was a little risky and they did have to wait for the temps to be above certain degree..that a lot of the longevity of the paint depended on the quality of the concrete...if it sweated a lot then the paint would probably come off quicker
they also had to paint some parts (including brick step in one garage) more than once because they were more porous and sucked up the paint...

the problem with this type of paint--or any type really in this situation I guess--is that steel-belted radial tires coming onto that paint can cause it to blister/melt and split..
contractor recommended not using the clear coat because of the slippery when wet nature and the tires' heat--that having it start to flake off was harder to repair than the paint's surface alone--that does not agree with what the other posted said--so maybe I misremembered--maybe it was just the slippery nature that made my husband not put it on...
so far ours looks pretty good--but when we wash it out, the floor is slippery--more than a normal concrete I think
we have a split 3-car garage
I drive straight in to my bay but my husband in a Tahoe has to make a turn into his -- more torque on his wheels and on the floor
I think his side is maybe showing some places where small pieces of paint have come off...

he plays golf each week with guy whose wife gave him that treatment for present last Christmas--after we had ours done...it was horrible...the guy she hired from Lowe's or Home Depot did not even read the directions...the finish was totally screwed up--made a horrible mess on his garage floor that he spend an entire weekend cleaning off...could not park his car on the floor because of what it would do to his tires...
so if you are doing it just read and understand the directions...