Which do yall prefer? We only have time to go to one so any advice about what you can do there, how expensive it is, etc. would be warmly welcomed.
Thanks, Kate

I prefer mondulkiri for the cool weather and better roads. Compared to Banlung, Sen Monorom is more developed and there are more guesthouses to choose from.

Haven't been to Mondulkiri yet.
I liked Ratanakiri. You could go for a trek in Virachey NP, visit the villages of ethnic minorities, maybe even overnight there, visit the gem mines (I didn't because of bad roads), see some waterfalls and Yaklom Lake or hire a boat to cruise the Tonle San.
The road up to Stung Treng is in an excellent, all- weather condition (7- 8USD by bus from Phnom Penh), from there to Ban Lung it's about 2 hours if the road is dry.