Sathorn was a nightmare for traffic and being there recently, traffic situation hasn't change but would definitely recommend to stay near the BTS. It's nice but the malls near by besides icon etc don't have as much to offer compared to Sukhumvit in my opinion.
Really enjoyed Ploenchit, especially inside noble as it was extremely easy to get around with a lot of more choice of things if I did need to quickly run an errand etc. I preferred Ploenchit over Sathorn personally. Just way more things overall in every aspect up there.