"Lower Sukhumvit" as it's known (roughly in, around, and between the Nana and Asoke intersections) is a lively, fun area. If you don't want to indulge in naughty entertainment you can easily avoid it. If you want to, well it's there for ya in all its, er... glory.

It's been a while since I checked rates, but you might also look at the Adelphi Suites on Sukhumvit Soi 8 (maybe a bit less upscale than the ones you mentioned?), and the Sofitel across from Soi 10. There's also the JW Marriott on Soi 2.

With any of those or the ones you mentioned you'll be right in the middle of the action, and similar walking distance to Nana and Asoke intersections (except Landmark, which is much closer to Nana).

Good luck.