Montezuma (on the Pacific Coast) is my favorite place on the planet. I believe the first two weekends of November there will be a film festival there (in the evenings) if you happen to be going at that time.
I like the Pacific side of the country more myself. Montezuma is a tiny tiny town and it's just great. Puerto Viejo is a pretty small town but it's huge compared to Montezuma.
I've been to Montezuma (over a dozen times) in November 3 different times and the weather has been amazingly good for being the end of the green (rainy) season).
Multiple waterfalls very close, another after a 2 hour hike up the beach. And a few more scattered around there.
Montezuma Pacific Hotel is THE best value in town (it's on Trip Advisor under B&Bs, maybe under Montezuma Pacifico) is great cheap and the staff is super friendly (A/C, WiFi, free coffee/tea in mornings, refrigerators, hot showers, big digital safes in rooms). I've stayed at this hotel 8 times(?) sometimes as much as 3 weeks. It's downtown but off the strip so it's not noisy; he downtown area is less that a few city blocks.
If you don't want to drive too much use Montezuma Expeditions and they'll provide transport to get you to and from SJO area for cheap; if you get in not early and have to spend the night, they have some hotel packages which are a real deal (pay the extra to upgrade to Casa Tago, it's worth the $5-ish, then probably $5 for A/C too). You could then rent something semi-local for a day or two (or just rent a 4x4).
Cabo Blanco national park is just south too (7 miles?) with daily bus transport (less than $2).
Edited: 8:28 pm, September 18, 2012