I prefer medium bowls. I wouldn't mind a small bowl to be able to smoke a pipe in the time an average cigarette lasts and I wouldn't mind a large bowl to every now and then spend a few hours straight of enjoying a favorite blend. But I do like my medium bowls though. They're just the right amount for me right now. I usually have myself a 45 minute to an hour or so smoke which is just perfect for me.
I like them all...I usually utilize a pipe size based on a time frame. Smaller pipes or Cafe Pipes as I like to call them for short smokes. Medium to large earlier in the day and bigger bowls for the final smoke.
I tend to lean towards medium to smaller elegant pipes. Im not a fan of large pipes because I am a clencher and I just find them too cumbersome in general. I do like small pipes for strong blends and have my eye set on a few group one to two sized pipes.
In general I lean toward the smaller sizes, both for smoke time (I prefer to keep a smoke to under :45) and, as I tend toward clenching, for comfort & grip. Although if I had a belly like Ganesh and multiple arms, I could obviate both of these issues and start smoking logs like hobie's monstrosity as pictured. ::
I tend to reach for what I consider medium to large pipes 5"-6.5" long with bowl 1.75 and taller.
My taste in pipe size and style has changed and evolved over the years, which is one of the many things I enjoy about pipe smoking.
Generally, medium to large. I'm buying a chimney with a big diameter where I can fill in 4-5 flakes (Irish Flake :P ). I wonder how it will go with something like Springbank 10 y.o. 100 Proof or Glenfarclas 105, but it's definitely going to be great.