Depending on your wants, both beaches are nice. HOWEVER, over the past month there have been torrential rains and many areas have been flooded. Also the roads have been washed out. I suggest you contact the hotels and other references about traveling there at this time. I go for business to San Jose and there are no major issues there.
Stayed at both properties earlier this year. A/C was down at Guanacast, preferred it anyway !!! Beautiful everything. Some may not like that it's isolate and not much happens (compared to busy and touristy Jaco - NB: Los Suenos is NOT in Jaco, but in nearby Touristy Herradura) Beach Club of JW Guanacaste is probably still "free" for the guest and is nice as well