If he is not in an environment (work and/or otherwise) where blade length would be an issue, and he is the outdoors type, then a 4 " blade (i.e. Endura, Military, Manix, etc.) would probably be good. Otherwise, a 3" blade (i.e. Delica, Paramilitary, Mini-Manix) may make more sense.
The ordering above is intentional. The Endura and Delica are FRN handles, wonderful knives, but less expensive because of the FRN handles (on the order of $40). The Military, Manix, Paramilitary, and Mini-Manix have G-10 handles, which are much nicer/grippier (especially outside in cold/wet weather), but are more on the order of $100 - $120. Many people start out with the less expensive FRN models, and perhaps move up - or, NOT - depends. I still use all of them. If weight is a factor, FRN is a great handle material since those models are very light weight (but still very tough; practically unbreakable!).
Plain edge vs. Serrated is an old debate, but definately a matter of personal choice - particulary with regard to the types of things he would use the knife for. There are benefits to both styles. Many on this forum (myself included) prefer plain edges, because they seem more versatile and are easier to sharpen. But, there are some applications where serrations are superior, without a doubt.
So, it may make the most sense to ask....so much for the element of surprise, but maybe a "gift certificate" (of even your own making on your
printer) to New Graham would be best ?
Good luck!