I actually setup open to my
line.
The reason I emphasize line is that while you're putting TO the hole, you're starting the ball ON your line.
Put another way: Every putt is a straight putt. You start your ball as straight as you can on your line to the hole.
The only time I aim at the hole is
a) short putts (inside 2 feet). Even then, if I detect a break, I'll play to the side of the hole (but still inside the hole).
b) long, long putts (25 feet or more) - but only if there's no obvious breaks. If it's simply subtle breaks the whole way, I'll just try to lag it close. I like 6" for my 2nd.
But back to the original question: As a straight-back-straight-through putter, I find it easier to keep my putter on line if I'm standing a little open.