Far smaller and less developed than Pattaya. Less options to do things.
The city configuration isn't great - a bit like an elongated rectangle. It stretches on both sides of a large road coming down from BKK. Going from one side to the other on foot is a pain in the a$$. By car, things get funny when you need to make a u-turn on the highway (dunno if it qualifies as a highway). Also it makes everything distant.
The train station area is currently under dev so it's a mess around there? New train station I believe.
Expats are the same as in Pattaya imo. A lot of old people. Some have money, others don't. Less mongers of course.
Thais are less friendly than in Pattaya imo. Rougher, less caring. I don't know why. My unverified theory has always been that the mentality there is heavily influence by the fact that they are the royal resort.
Bars are divided in 3 areas. Soi Bintabaht is more for tourists, soi 80 is more for expats and Wonderland has always been more or less dead as far as I know.
Lack of laundromats in the center. This is a real pain in the butt.
I moved to Phuket coz I wanted to enjoy decent beaches and pristine water. Didn't regret it. Hua Hin had become dull to me. It's a bit of a depressing town honestly unless you enjoy slow life.
Great immigration office at Blueport. That's really a plus.
It is nice to spend a couple of weeks there and visit the different temples and hilltops. Imo after 6 months you'll get bored. But who knows... You should go visit if you haven't. Best way to figure out if you'd like it there full time.