Light Balance - mostly because it is genuinely unique in the line up of semi final acts. There's a couple of acts that could got the pimp spot - but I'm betting it's Bars and Melody (like others have said) - and they're pretty much a dead cert to go through if they are in that spot. If they aren't, there's a chance that Lettice or Eva could get through, simply because they both are very talented.
My prediction, the Irish dance troupe get the first death slot, they put someone like Keiran and Sarah next, followed by the DJ, Eva, the fire act, Toju and Light Balance. I suspect Lettice and B&M are the most likely last two acts of the evening, and are the two most likely to get through. I'd put Light Balance or Eva in the third place spot. Both will miss out if Lettice is in one of the runner up positions at the end of the night. It's a shame, cos I think this is one of the better SF line ups - 2 nights ago, LB would have walked it into the final. Now, I think they could miss out on top 3 entirely. I hope not though.