I am looking into buying an 18-gauge brad nailer. What is the difference between all the air compressors on the market? I see 1hp, 3hp, 5hp, etc. For simple projects around the house like installing trim, moulding, etc. what size air compressor should I get? Is it OK to go with the smallest option?

I noticed Lowe's also has smaller air canisters that are designed for nailing guns. Are these worth looking into? They don't cost much less than the smallest compressor, and there's the added charge of replacing the cans when they're dead.

Any suggestions would be helpful.

For a simple 18ga brad nailer you do not need that much cfms. CFMs is the measurement of air volume provided to the tool through the air lines. The amount of bradding at one time and the amount of air cfms and psi are what is important. If you are doing small simple projects a small pancake compressor will probably supply the amount of air required. If you are going to be doing more than a couple hours at a time, I would go with the larger compressors. Remember, you will not have to listen to the larger compressor run as often. With the small compressor, it will cut on and run much more frequently.