The most important thing in a letter is definitely not their degree, but the content of the letter. If your inpatient attending can write you a strong letter that details what you did while inpatient (hence it's not generic) and voice their support, I'd go with that. If the outpatient physician can offer you that, then go with that letter. That being said, you did mention that you did not honor inpatient IM - if you think the inpatient physician can write you a good letter that would be very beneficial.