Is there anything inherently different between 15amp and 20amp outlets? Outlets labeled 20a are about 3-4 times more expensive than the ones labeled 15a. My buddy with a fair amount of experience advises me to buy 15a outlets and hook them up to my 12 gauge wire running back to 20amp breakers. While this may not follow the label he says people do it all the time and there's no issue. Good advice?

Some 15 amp receptacles have the wire (14 gage ) push into holes on the back of it , the 12 gage wire will not fit into these holes ,

But if I am content to use the screws on the side of the outlet instead of the push-in holes?

Using all 15 amp devices on a 20 amp circuit builds in some added protection by derating the circuit as 15 amp outlets will limit the size of any appliance to 15 amps. Only using 20 amp outlets where a 20 amp appliance is, these have the two flat blades perpendicular, will keep the expense down and reduce risk of overloading the cable.

Always use the side screw terminals or the clamping type that tightens with a screw. The push in style is a popular cause of service calls.

Yes there's a diff bet the two outlet the 15A can accommodate an appliance with amp rating up to 15A only, if over up to 20A you are overloading the receptacle but not the cable if the cable is designed to handle a 20A load, but if your appliance are all rated 15A and below there's no harm if using an outlet rated 15A connected to a cable rated for 20A load.

What appliances these days draw more than 15A 110v? A hair dryer is the only one I can think of. Even most plug in heaters don't exceed 15A. Are there others I am not thinking of? Because, assuming jobberknoll is correct, I am inclined to go with 15A outlets (bc they're cheaper) wired to 12ga wire and a 20A circuit breaker. That way I am in less danger of overloading the whole circuit from running appliances at the same time off multiple outlets.

Correct me if am wrong but now a days most of appliances are pure electronics not electro mechanical which means less amperage, anyway I check some of my appliance w/c rate 15A below ,say personnal ref, water dispenser , mini component, deskfan, standfan, desktop computers, radios, and many more , anyway if the amount diff is not that much for safety just go with the 20A receptacle according to the design.