In Mount And Blade Warband which would be the best Country to go with

Personally, I like the new faction, the Sarranid Sultanate. Mostly because they're new and I've played with the others in the original M&B, but also because their heavy cavalry, the mamluks, are amazingly useful and durable.
Here's a guide to the other factions, hopefully you can choose one for yourself based on your preferred play style.