Well, it seems the winner is the A1500--it hasn't even been mentioned in the least popular thread!
But it wasn't separate Amiga model at all.. just normal A2000 with extra drive and removable sticker
Only sold in UK.
For the main question I'd say A600 too. It didn't sell much as at that time it didn't offer that much more than A500 in practise. And Amiga's most popular days were ending at that time. Although I think it was the last Amiga model sold in "normal" shops here (Finland). A1200 was only sold in dedicated shops, but as it was that much better than older models, it got more popular among the hobbyists.
But nowadays the situation is a bit distorted. I guess the A600 is one of the most popular models to get into retro computing...
