My friend and guildie, DoubleUnder, also has an Engineer that he loves to run sPvP with. He went a different than I did, which is the beauty of a versatile class. He wrote up his build on our guild forums, which I have reposted below, with his permission:
So when I started GW2, the last class I wanted to play was the Engineer. This was simply because of the learning curve to understand how to use all the elixirs, turrets and kits worked seemed like a lot, and it seemed like a difficult task to mesh all the utilities together for a good build.
What I found using the Bursty Roamer Spec was that I had good CC and a some burst, but in no way would I be able to hold a point, or go head to head with a 100 Blades Warrior. Most of all......those damn thieves.....always spamming the Heartseeker or Backstab. The Bursty Roamer had no place in a fight against a thief.
So I set out to Theory Craft a build that could not only deal damage, but could go head to head with the DPS classes.
While Theory Crafting this build, I wanted it to be simple, yet potent. So I focused on Elixirs as my utilities. Not only do they provide great buffs, but they can make you immune to damage and remove conditions.
The ability to convert thief conditions and necro conditions into your own buffs is huge. Just let your opponent stack them on you (while burning their own cooldowns) and now you have the advantage, your opponent basically making you stronger.
I put 20 points into Alchemy for the +20% Boon duration and the 20% increased cooldown to elixirs. This is especially important to getting your heal off as fast as possible.
I took 20 points into Inventions for the added toughness, and the 20% increase cooldown to the shield abilities. (The Shield will be your best friend against thieves and warriors).
I put 30 points into Precision to get the Pistol ability increase cooldown, pistol range increase and piercing shots with pistol (allows you to hit your target and whatever is behind it).
(We need another screenshot here, DU.)
For my runes I took 2 Runes of the Monk and 2 Runes of the Water for +50 Healing and another 30% Boon duration.
My Might buff now lasts twice as long as the Elixir B cooldown, allowing me to have permanent might and stacking it in duration. This also extends my other 4 buffs a great length.
For the last two runes I took Rune of Dwayna for the +20% health regen duration.
And don't forget, throwing your AOE toolbelt elixirs helps to maintain buffs and heals when your main utilities are on cooldown. They also give buffs to your allies during a group fight.
I took the Soldiers Amulet for the added power and toughness. Because this build is all about staying alive, so toughness is important. And toughness is my highest stat on my character, allowing me to survive a long time (buffs help a lot also).
This is not a high crit or DPS build. But you will live a long time once you grasp the rotation and understand how to be defensive. I can outlast a toughness spec warrior (if I play it smart) and no longer do thieves ruin me in 5 seconds. The full build is here. It took me hours to theory craft this build, and comments and criticism is appreciated and welcome!