Two very different musicians, especially if one considers the totality of their respective contributions to Jazz. Both important Jazz players, but ultimately Miles is deserving of the title as one of the giants of Jazz. Baker was a beautifully introspective player with a distinctive way with a melody. But, so was Miles…. when he chose to be. His tonal “palette” was much more wide ranging and his musical persona changed a great deal over the course of his career. He was one of the great innovators in Jazz having influenced players in genres outside the “mainstream”, which is where Baker “lived” pretty much his entire career.
From the standpoint of instrumental technique and as demonstrated by their recordings, while it could be argued that Baker was the more “refined” trumpet player given that soothing and warm quality to his tone (itself a sign of good instrumental control), Miles’ showed much wider dynamic range and sheer technical facility. His expressivity seemed to be less dependent on his “sound”.