Rollerball would have to be capped--probably the ballpoint is a better choice if you want a "daily user" as opposed to a "collector piece".
Obviously, I like the "thank you pen", I helped design it. The aero is also a favorite pen. The statement that it leaves more meat is correct, but meat is weighed by the pound (in other words, more meat=heavier). Honestly, I have never weighed the pens and they both feel very good, in the hand.
Be sure to replace the refill with a Schmidt 9000 and you will gift a fine writing experience with any of the pens mentioned above.
Good luck!! Enjoy making the gift!!
Ed