Heading off to Pattaya from Surin by road during a weekday. Any recommendations as best route by road?

Any suggestions appreciated.

I use route 24. Out of Surin towards Prasat. Turn right at major crossroads. It becomes a dual carriage way after 30 kms. Fast with few BIB blocks. after 200 kms (distances approx) turn left towards Chachongsao/Pattaya route 304. Beware the fork; (right takes you to Chachongsao) you stay left at Kabinburi.

Personally I would take to Sa Keaw route.

Avoid the 24 by turning left at the Krasang crossroads to Prakhonchai via Plapplachai.

Straight over PKC lights on the 219 going to Ban Kruat and Lahansai. Turn left in Lahansai to Non Din Deng and onto Wattana Nakhon. There you join the 33/331 (dual carriageway all the way to Pattaya) - after about 70km you join the 304 and onto Pattaya - either fork left on the 304 (signed for Sattahip) or onto Chachoengsao and the motowat No7 into Pattaya.

after about 70km you join the 304 and onto Pattaya - either fork left on the 304 (signed for Sattahip) or onto Chachoengsao and the motowat No7 into Pattaya.

I once forked to Chachaengsao (about a year and a half ago?).

At this time it was a terrible experience.

Crowded as mad, dangerous construction sites (open excavations, dirt roads) etc. pp.

Maybe things have improved, but will never use it again.

Better be shaken on #331 going south (or cling to the right lane as most do)

One of the routes that Google computes seems to come close to what @Jip99 suggests in post #3 ?

Just that it leaves #33 to shortcut via #359 towards #304.

As I do know the route only from the point on #304 I can not comment on the quality of these roads.

The map:

https://goo.gl/maps/T9iB0

Hope you see a blue highlighted route, 429 km (as I do).

The time estimates of Google are usually a bit high.

Start and endpoint are somewhat arbitrary.

There are different routes from #331 to Pattaya/Jomtien.

Depends on where you actually want to go in Pattaya.