depends if you are interested in 3d really?. if so i'd get the samsung as it's a highly rated 3dtv that would be more futureproofed, the sony is 2d only, and to my knowledge should have similar picture quality..
both have similar features (3d aside) including freeview hd, so there's more value in buying the samsung imo, although you would need a 3d blu-ray player/ps3 also if you want to watch 3d movies or play 3d games, or sky 3d..
i dont know if comet sell the lg42le8900? but if they do and presuming it's within budget i'd check it out as it's a non 3d, rear led lcd set that's said to be excellent. i'd say it would give you the best picture quality from the three..
if you could accomodate a 50in tv then i'd also check out the non 3d lg plasmas which are also excellent