I run a hybrid support build.
http://gw2skills.net...m0geUf9yXRKyfjB
That's basically the build I use. Some things change as the situation requires, but one thing that NEVER changes is eGun. It is always on my bar. Always.
Flamethrower usually occupies one of the slots that Rocket Boots and Elixir B are in. I left both of them there to showcase them, but only one of them is usually actually on my bar. If I'm expecting a need for a stunbreaker or another escape, RB is equipped. If I'll need the boons then eB is equipped. For bosses, the set-up shown is usually exactly what I use.
For non-boss fights, more often than not I have RBoots there (with the FT), because it has offense (toolbelt), it has defense (stunbreaker), it has mobility (umm.... they're rocket boots!), and finally it's a blast finisher. One of the best utility skills Engy has IMO.
The second (20 pt) major traits in both Alchemy and Tools are interchangeable based on needs.
Running around the world? Speedy Kits in Tools. (This is only when I have a long way to run and don't want to stop. For general purposes, eB and MedKit5 are enough.)
That build brings a ton of support to the table. Does your group need even more? Packaged Stimulants in Tools and Form 409 in Alchemy (with eGun, eB and eR - no flamethrower in this situation).
Headed into WvW? Sometimes I'll use Protection Injection or Self Regulating Defenses in Alchemy instead.
You get the idea.
The support that eGun brings with Kit Refinement is amazing. Perma-Super Elixir for AoE healing, on demand condition removal and a perma-light field (more condition removal with projectiles) is fantastic support. Coupled with Supply Drop, anything from the MedKit, and eGun 1-3, there are few builds that can offer as much support.
For large groups of mobs up close, FT is my kit. If you can handle proximity it's the best DPS in my load. For groups of mobs at range I use my pistol because Coated Bullets is awesome. For bosses and heavy hitters I have eGun for perma-weakness.
The DPS obviously isn't what a Grenadier will put out, but it isn't terrible either, and the versatility and support offered more than makes up for it in my mind.
There are some rare occasions when I'll use a rifle instead, but only if CC is needed and no one else can handle it. I simply don't like the rifle much, but I'll use it if I have to. The reason I don't like the rifle doesn't actually have anything to do with the rifle itself. I dislike the rifle because it prevents me from using my shield.
Projectile reflection, a knockback, and a blast finisher all on one skill.
A two second block, a stun or an AoE daze in a line (which could be two dazes if done properly) and a projectile finisher on the other skill.
In my opinion the Engineer's shield has one of the best sets of skills in the entire game, and it does it all on only two buttons.