Like many of the responses here, as well as from the OP, the crux of this question for me is the psychological impact.
i've been primarily anally oriented sexually from my childhood. For me, the underlying message when a guy is wanting me anally is His expression of need/desire to open a vulnerable part of me in order to penetrate and put a part of Himself in me.
i am 'bottom/sub' emotionally, so am particularly drawn to Top/Dom types. i see the draw as a natural phenomenon of opposites attracting.
For me, either way... whether He spreads me or wants me to spread myself, both of those are expressions of His need and desire to have me vulnerable to His penetration, to give Him access to me. So, for me the distinction in this question would be who initiates. I.e., in the Top/bottom Dom/sub dynamic, i'd likely not be presenting myself without His initiation, so the how of it is less of a factor than the why of it.
Either way, whether He asks me to spread, or spreads me Himself, both are expressions of HIs need/desire and have an equal impact on me depending on His attitude. The attitude is key for me in how He affects me emotionally. A clinical attitude doesn't open me. A forceful attitude closes me, shuts me down. Overt need/lust opens me. Subtle but persistent attitude opens me the deepest. i think the "subtle but persistent" approach has the most impact on me because when a Top/Dom exposes His own need/desire to me, i have a seemingly autonomic response in kind, like i cannot help it. It's almost hypnotic.