On my way to Vientiane, I stopped a couple of days in Udon Thani.
Pretty decent city honestly. Not too big, not to small. Nice people everywhere.
Enough bars to chill (girls are the same as in Pattaya, prices are much lower though), enough shops to buy whatever you'd like.
Plenty of Westerners - mostly old people, polite and willing to share their knowledge of Udon.
Extremely underrated imo.