Well, purely from a technical stand point, the Yang-37 doesn't have needle at sea bottom, double punch to the ears, fan through the back (although fair lady works shuttles is similar to this), hitting the tiger postures right&left, snake darts tounge....uh...that's all I can think of for the time being.
I practice the 37 more than any other form, I really like it. But if I have more time to spare, I practice the 108 because of the extra movements mentioned and there are some transition motions that the Yang-37 doesn't have (eg the motion right after fan through the back, there is a turn and chop with fist posture, and the transition right between that and the rollback-deflect-intercept-punch sequence is a nice set of movements that repeats a few times in the form...).
But at the end of the day, energy is energy. Whatever form you do, it's not enough to do just that for developing real Taiji skill. Must do standing meditation quite a lot, along with push hands and silk reeling.
Just sharing what I've learned and am still learning,
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