I responded, somewhat tongue in cheek: But which does God prefer?... (Shades of the old traditionalist joke: you worship God as you want to, we'll worship Him as He wants us to...)
However, he is not one to leave it there, and my ducking his question about what I thought by saying that it's not my opinion which counts was not enough for him.
So I thought I'd better post on it: it will take a little longer than Twitter allows.
So what do I think? My instinct is that Sunday morning is the better time for Mass. That is the time-honoured practice of the Church and that alone carries a lot of weight for me.
I certainly understand that in cases of necessity, a Saturday evening Mass can mean that one can fulfil one's obligation when one might otherwise not be able to do so - and have indeed taken advantage of that innovation myself.
And I actively like Midnight Mass for Christmas or Easter.
I am also aware that today (and quite frequently) I am going to Mass on a Sunday afternoon, which again is not very traditional: however it is the only time on a Sunday when an EF Mass is celebrated within 60 miles of where I live.
But I think, if I am fair, that part of my disinclination (and I won't put it more strongly than that) to go to Saturday evening Masses, is that in my experience many who go then do so in order to leave Sunday free for other activities - and that does strike me as problematic. And clearly that is a prejudice based on a small sample, and does not by any means hold good for all who attend then. But, as I say, if I am to be honest, I think that is at least half of my reservation.