Having just returned from 2 weeks in Patong, being my first trip in low season, the bars in general were very very quiet.
As Nicke has mentioned, still lots of people walking down Bangla but the Sois were quiet. The two bars which always seem to be busy, all through the year, are Kangaroo and Aussie Bar. The latter is a great place to watch a sporting event and we just about found a seat to watch Super Rugby final.
Kangaroo is a great bar too, well run, with great staff. The place is always packed.
Soi Eric was quiet in general - would say MTB by far the busiest. I think maybe the bar next door had about 5 customers in a week! I have heard it is quiet too during high season.
Soi Tiger - arguably has the best looking girls but most of the bars were quiet. Not cheap here with LDs costing 200 baht.
Hollywood still packed with decent looking women, found Tiger Disco slightly less busy.
I had some decent weather, better than I was expecting. Would return for sure at this time of the year.