Costa Rica in January for 3 weeks

Quick response, I've briefly stopped in Nosara once, but have visited Tamarindo several times and stayed in/around various places in the area. Both places are known for surfing, but Tamarindo is an actual City on the beach with a large shopping district and ton of restaurants, bars, beach clubs, etc. Nosara is a town with beach access, but more remote and low key.

Really depends what you want in your stay, more options of things to visit around Tamarindo, but you can easily access all of the fun outdoors Costa Rica stuff in Nosara. If Tamarindo, look at Playa Langosta just south, little less developed but still easy access to the City.

Also Nosara is more remote and probably 3 hours from Liberia In't Airport, Tamarindo is only 1.5 hour from the airport.

We went a couple of years ago and did a few days in Arenal (stayed at the Springs Resort) and then rented a VRBO in Playa Conchal. Thoroughly enjoyed both and would not have changed a thing. Conchal has a white sand beach which not the norm for the pacific side, but was awesome. Playa Brasalito is about 10 min away and was also really cool. We drove down to Tamarindo one day and it was cool, but much busier.

I went 2 years ago for 10 days. My wife and I. We were 31 at the time.

Stayed in Santa Teresa on the Nacoya Peninsula.

It's a mofo to get there unless you fly the green airlines flight to the little regional airport there. The drive from the Puntarenas ferry was like being on the worst dirt roads you've ever been on for 2+ hours.

Santa Teresa is awesome though. I loved it. Watch the sun set over the Pacific every night. Tough to beat. One thing we commented on is how old we felt in ST. It was like every person there was an expat 25 years old. There were very few families there and a lot of people 30 and under. Could have had a lot of fun there in my college years.

Cant help yet. Going with 16 folks in September for a BD party. Have a house rented on a hill overlooking the water. Its called Compass House in Tamarindo. We have an excursion planned every day in/around Tamarindo. We have all been to the jungle part of CR, so this will be a new experience.