Best Engineering item.. I guess that is a tough one, but here is my humble opinion as a 60 MC/BWL Hunter/Goblin Engineer. In terms of PVE Raid content it's the repair both easily. Now then for PVP It's honestly a tie, if I don't say the Deathray I'll catch no end of flak =P but personally the Gnomish Mind Control cap is priceless. Many horde on the Argent Dawn Server (or the "The Alliance Gankfest Server" as someone quoted it on this thread) have learned not to be caught flagged near their windriders if I'm nearby. Yes you can MC Cap someone turning them into a pet and force them to attack their own Windrider and watch them get absolutely destroyed, lots of fun! In terms of money making a lot will tell you Core Marksman's Rifles which is pretty much at this point a lie. The 6 cores are hard enough to come by if you are not in a top end guild on your server, and if you are especially since 1.6 you are not gonna be able to get the cores to make a rifle to sell unless the money is going to bank. Most of my money from Engineering is Sniper Scopes to be honest, sure if I can buy the cores in AH I will gladly make a Core Marksmans Rifle and put up in AH =). As for a quick note, someone saying it was the second best weapon in terms of DPS is not true. Rhok'Delar (Hunter Epic), Blastshot Rifle and Striker's Mark all out DPS the Core Marksman. But on another note nothing is quite as sexah as the giant silver Supersoaker with a huge searchlight on top of it either, not even the flower sprouting hunter epic bow. But these are all my opinions as well, good luck and have fun blowing yourselves up with Engineering!