Mesmer heroes are the best, but I think people get carried away acting like player Mesmers are alone on top of the mountain for PvE classes. I typed up this tier list in the "guide to PvE" post someone made earlier.
P/P Deadeye, Shortbow Renegade, Scepter/Torch Scourge are all gods in solo play if built right. Scourge is probably the best, in trailblazer gear you can solo anything by facetanking it. Renegade is up there as well but has to kite some.. P/P deadeye is nice, its very mobile, heals itself, and gives itself boons.Currently holosmith is the go-to choice for engi, having insane power dps in both sPvP and PvE. Holosmith is easily one of the best dps classes. Core engineer is not quite as good as it's elite counterpart, but then again anet wants you to buy their shit so no surprise there.