I go to Ha Ha after shopping with friends. It is perfectly nice later but we never got into the habit of going there (sadly, as it used to be a place to avoid when it was Yates, but is now really nice). I'd recommend it for food on a Saturday, or a lazy summer afternoon (it has a terrace with a view of a park and old stately home, NOT a big road, which is rare in London).

I am in late 20's, and visited Ha! Ha! twice on a Saturday evening with a group of lads. It has nice decor and bar design. I managed to find a few seats downstairs. The prices are reasonable. Ha! Ha! is good for sitting down and chatting. After 10pm, the bar attempts to transform into a livelier and noisy dance bar.

Ha! Ha! Bar & Canteen is a chain pub, but in a nice way. Big wooden tables, long leather sofas and not too pricey drinks. The food's good too - burgers and salads and stuff.
I wouldn't come to Ha! Ha! Bar & Canteen for a big night out, but it's a nice place to kick back for a couple.