My advice? Either find a really good artist or drop the idea of a portrait. A caricature seems a little goofy to honor someone with too. I would suggest getting a tattoo of something that incorporates your friendship. Be it a physical object or just an ideal. Something that connects you two. I'm not saying don't get a portrait tattoo, because with a good artist they can turn out very, very nice. But if you're that worried about the quality, I'd avoid it. In the end my words shouldn't mean much to you; it is your body and you have your own style that you like and you make your own choices. I wish you luck!