My NEW preference is the scalar with charge +4/3 that is being postulated as an explanation for the top-antitop asymmetry.
There are some published papers pursuing this idea, such as http://arxiv.org/abs/1103.2757 or http://arxiv.org/abs/0912.0972 and a couple of mini reviews http://arxiv.org/abs/1108.3341 http://arxiv.org/abs/1107.0841.
As of today I can not tell which papers are the most relevant (see an explicit question in TP.stackexchange). I think that they have a potential to explain some of the other observations because the charge in some GUT models has a contribution from B-L and a contribution from SU(2) chiral groups, so the +4/3 is nor really so exotic.
In any case, take my answer with a bit of salt. As the uppercase acrostic indicates in the first paragraph, I also have some personal motivations to support models along this line, because I tripped into these pesky +4/3 things back in 2005 and I really want to understand how they fit.
This post imported from StackExchange Physics at 2014-06-07 05:13 (UCT), posted by SE-user arivero