Basicallyan Audio interface has a soundcard in it usually. So its like an awesome USB soundcard that can handle a guitar sometimes and usually a MIC. Different Audio interfaces have different quality soundcards, handling it quicker or better than eachother. In other words, read reviews from legit places. Audio Interfaces have Soundcards and I'm guessing will always be better than some rinky dink built in sound card or USB external.
Many Audio Interfaces come with a DAW. EG: Ableton, Protools, Presonus
i think you should have a better -external interface.Lower latency,better timing,better audio drivers,less problems(clicks-pops etc..),better clock,better monitoring options,preamps,midi.