I'm fortunate to have a gifted therapist locally that I use on a regular basis. Often I'll need to take a couple aleve/advill at bed time because I might be beat up from a workout and a massage on the same day. I'm not afraid of being a little sore, or enduring a little pain and I find it frustrating when a therapist is on the "knot" or trigger point, but can't break it down.
The muscles btwn the ribs, the intercostals, the supraspinatus muscle in the upper back, and the hip flexors - the iliacus and psoas are particularly painful to have work done on, but so important. I forgot the armpit w the pecs, subscapularis, and teres major - again very sensitive area, but necessary for a full range of motion, and reducing the chances of torn rotator cuffs. The hip flexors are avoided by most every therapist, unfortunately.