Over 2 years ago now I started a new job requiring me to carry a pen basically at all times. When starting out I think I tried almost all of the popular office brands but there was something I didn't like about all of them.
My criteria became:
Slides in a pocket easily
After all the others, too many to name here, I first settled on Zebra Brand pens and tried out all of the versions that were available at local stores.
Zebra F-301 models which are usually $6 for a 2-pack:
They fit almost all my needs, however, I didn't like he plastic parts that were used. So I checked Amazon to see if Zebra made any other models that aren't carried locally and found that there is one.
Zebra F-701 under $10 each:
The pens pictured are the ones I have been carrying and using daily for over 2 years and they have held up well with only slight visible wear on the body and some pot marks on the clip.
All the visible parts are metal except for a small ring at the top and there are some plastic parts inside but I haven't had any problems with them.
I also like that they are refillable with the standard Zebra Ballpoint F-Refills available at most major stores or Amazon. I've put 2 refills through both pens so far.
Also, with the solid metal body, they can be used as a last ditch self defense implement if needed. A task most common pens wouldn't be able to handle.
Right now they are under $7 on Amazon