I've spent a lot of time in CR (almost retired there a few years ago). It depends on if you want beach, mountians, etc. I normally stay in SJ and day trip where ever I want to go-it's only a two-hour bus ride to about anywhere. Rainforests, Beach, Volcanoes. The other option is to stay up around Arenal and it's just a short trip to the beach. There is just so much to do all over the place, I don't know that I would stay just on the coast. My ultimate trip would include a few days in SJ, a day or two around Arenal (including a day at Tabacon) and a few days on the beach (a dozen decent ones to choose from). Cool day trips are of course the Aerial Tram, there is a boat trip out of Punteranas (can't think of the name right now) that is nice-a day on a private island, and the river trips are cool (ever seen a Jesus Lizard?). And if it's just a bunch of guys, head down to the Blue Marlin Bar in SJ-it's hooker HQ for Costa Rica. I'm not saying you should partake, but it is an amazing sight.
And learn the phrase 'La queta por favor' (sp?). When you're out, a server will never bring you your check-you'll sit there all night if you don't ask for it-Costa Ricans (especially the Ticas) are very timid.
Oh man, now I'm wanting an Imperial...
