Originally Posted by
amk
Think about comfort first so choose a pen that will feel good in the hand - not too thin or fat for your hands, not too heavy for you to feel comfortable writing with it for a while.
Choose a pen that takes a standard refill size. Then do some research - even if that just means buying every refill that fits, and trying them all out till you find the one you're happiest with.
Decide on your style. You may want sober black: all metal: black with a twist (I have a lovely Jean Pierre Lepine ballpoint, nicely understated black but with a wonderful corkscrew twist clip): single colour: or vibrant colour. Depends who your clients are and what your image is.
Then take a good look around. Waterman Carene (rollerball, very nice) and Parker Duofold can be recommended, Pelikan (various sizes) or Mont Blanc, or Lamy (some very attractive Lamy 2000 ballpoint versions including Titanium, matt black, steel and yew wood) but if you want a minimalist and modernist style you could also look at Venvstas, a French brand that's not so well known.