The bottom line is that either choice serves the function of getting doors and drawers open. There are kitchens that do all of one or the other. Most people do a mix, commonly knobs on top and pulls on the bottom, but there isn't any solidly good reason for that.

I like pulls on the bottom because it seems more ergonomic to me, but we've had knobs on the bottom and that worked fine too. Actually, I think we had knobs on all the doors (incl. the bottom cabs when they were all doors) and pulls on all the drawers. It's really a matter of preference and looks. Now that I think about it, we've had knobs on various dresser drawers over the years and I found those drawers harder more time consuming to open and close.

One of the nice things about this forum is that there are photos of the different choices people have made so you can look and see what you like or don't. Try these to start;

http://ths.gardenweb.com/forums/load/kitchbath/msg0116075221147.html

http://ths.gardenweb.com/forums/load/kitchbath/msg0114053120568.html

Here is a link that might be useful: Show me your knobs and pulls