If you are like most people getting ready to do a garage floor you are doing a lot of research.  Some of this information may be redundant and some may conflict with what others recommend.  This is not intended to discount any research that you have already done and learned from.  There generally is more than one way to install epoxy, but, most what you read about preparation is probably true.  Some sites will tell you to grind your floor, some will say acid etching is fine.  Then you start hearing about primers, and build coats (same as intermediate coat) of epoxy, and whether to top coat with epoxy or urethane.  The list goes on and on.  It is wise to do your homework, and most of the research you do will probably be correct, so what do you go with?  Which is the most asked question, What do you recommend?  I have been installing floors for a long time and have used many different products.  Epoxy is a formulation of different chemicals with additives for specific purposes which is meant to react to many different conditions.  So to say one product or preparation method is the best is not always possible.  Below are examples and answers to many common asked questions.

Yes!!! Preparation is critical.  And yes, it is possible to have a successful long lasting durable floor without doing a whole lot.  BUT WHY TAKE THE CHANCE!  Especially if you plan on enjoying it for yourself.  If you can rent a grinder do it.  If not, it is highly suggested the you at least degrease and acid etch the floor.  Many people ask, in one way or another, if preparation is minimal is there a system or epoxy which is better than others?  Answer is yes, at least use AD134 primer and AD311 top coat.  Two coats of both, or at least two coats of either of the two is even better.  If you're going to purchase a big box store water based epoxy kit then just buy the AD134 and be done with it.  It is by far a better product but it does have an odor.  If you want an odorless epoxy then AD5 is a substitute water based epoxy but AD Polymer's water based epoxy does have a higher resin (solids) content than most.  Or, better yet, go with AD0LVP high solids epoxy. However, if there is grease on the concrete, that will need to come off with degreaser, before coated. 

To prime or not to prime.  Priming offers the best chance for adhesion and reduce occurrences of air bubbles.  AD134 is a great epoxy primer.  The solvent (xylene) in AD134 helps adhere because as the epoxy is drying the concrete is absorbing the xylene out of the epoxy  pulling the solids (resin) material down allowing the epoxy resin to embed itself into the concrete.  Water based products work the same way except water evaporates quicker than solvents which means there is less opportunity for the bonding process to take place.  That is true for absorption rate as well.  Concrete is absorbing the water at a faster rate, again lessening the opportunity to benefit from the bonding process.  Odor is present with the AD134. Only last a short time and is strongest just after applying.  Another primer is available and that is AD0LVP.  Much higher solids but does have some xylene with much less odor.  This is used and was formulated primarily for concrete that is less than perfect in the sense of pits and small cracks.  It is heavier so it helps hide those imperfection.  Still, AD811 crack and joint filler may be desired. 

About top coating

Urethane top coat or not?  One or two coats?  Most company's will say two coats of urethane because it is a safe way to ensure there is complete coverage of the floor and if coating over chips, then two coats will give smoother finish.  I agree.  If chip flakes are used, especially heavy broadcast, then two coats will help reduce the profile from the chips.  If not using chips, and you are just coating a single color floor then one coat can be sufficient.  It is completely up to the installer.  AD311 has an odor but it is very high performance.  See data sheet for specs.  Polyaspartic is available but not recommended if not familiar with it. I sell two types of polyaspartic urethane, AD331 and AD339, but only one is made available.  Unless otherwise asked.  AD331 dries extremely fast.  8-10 min working life.  Generally used for very small jobs that require very fast turn around.  Bathroom in store etc...  Or countertops. 

One major notable, in regards to top coating, if you use a chip broadcast of .05 x sqft. or more then you must scrape the floor with an 14" floor scraper or similar tool, after it is dry.  If a small area is coated such as a residential bathroom, then simply a hand held putty knife will be fine for scraping.  Scraping will knock-down any sharp flakes that may be stacked on one another that could create a point after the urethane is dry.  The more chips the more texture, which means the more urethane you may want, to leave a smoother finish, depending on the desired feel.  If texture if desired, for a more slip-resistant floor, then one coat of AD311 will leave a profile from chip flakes or even two thin coats of AD311 works out very well.