Depends I suppose. The first one in the morning is always welcome. The last before toddling off to bed is nice also. The ones in between are good. I suppose the the first one after dinner, accompanied by a glass of port and a great book is the most enjoyable. But, a late summer's evening on the deck with the lowering sun? Great. Wintertime? Hands down its in front of the fireplace, in my chair with book and port. Late afternoon shooting loons, not a sound but the birds? That's very special.
There just isn't a favorite time. They're all good.