Coincidentally I have been to class on this subject this past week. I have stained 3 floors and just bought the stain to do my garage floor.
Acid stains react with the lime in the concrete and color the concrete itself. They are not a layer of color like a paint.
This means that you will still have the problem of oil and gas staining the concrete so you will need to seal it someway.
Most good concrete sealers are xylene based and professionals typically won't use water/acrylic based sealers.
I intend to seal mine but I don't intend to add a clear epoxy coat since that gives you something extra to lift or wear off.
Since the color is in the concrete itself you should not get a wear pattern develop.
Speaking of color in the concrete, there is also a broadcast color powder that is added to the wet concrete and trowelled in. I just did 3000 sq ft of my house that and then used a textured roller to give it a pattern like rock. This still has to be sealed.
You can also have color added in the truck when your concrete is poured. It is only about $3 a yard more than uncolored concrete.
In the past 3 months I have done all of these methods. I have been learning a lot!!!!
P.S. you can mix and match these techniques and you can also add layers of color to get different effects. On my house I used the broadcast method of color mixing 2 different colors and now I am in the process of adding a layer of acid stain to get a deeper effect. My test section looked fabulous. I will be finishing and sealing the balance this weekend. I will post pics once it is doen.