There are no Hasbro Sub-lines that I do not regret not buying. In recent years, the only three sub-lines I've passed on are: Force Battlers, Galatic Heroes, Star Wars Choppers.
I will continue to pass on Galactic Heroes. I will also be passing on Mighty Muggs.
I kinda wish I had passed on the Star Wars Transformers sub-line and the 2" Unleashed Sub-line, but I'm deep into collecting those now so I can't just stop (damn OCD).
I did feel regret earlier this year with the 3" Titanium Vehicles, I had not been getting those and in the past six months I have caught up to the point where I only need three of the four WalMart 5-packs and somewhere in the ball-park of 20 individually carded ships. I'm not in any rush to be 100% caught-up with these, so it's fun to try to pick up more when 3.75" figures are in a lull.