like everyone else has said engi is just awesome with the different things it can provide, blacksmithing is good and starts to pull head when we get epic gems (tho is a little ahead if your class favours secondary stats over primary)
Synapse Springs is 1920 main stat for 10 seconds on a 1 minute cooldown. A non-upgraded epic trinket gives 5.105 main stat (5500 if 2/2 upgrades) for 20 seconds, also on a 1 minute cooldown. The honor trinket gives you over 4k main stat for 20 seconds. The Springs pail in comparison to the trinkets, and you can't even stack the springs with a trinket. Engineering isn't a good profession for rated PvP because you can't stack the springs with the trinkets and one of it's other main perks (nitro boosts) isn't allowed in rated PvP. I'd rank it below any other crafting profession (but above any gathering professions of course), because those at least give you the regular 320 stat benefit at times where you need it most (burst), whereas Engineering can't do this. Out of the crafting professions Blacksmithing and Jewelcrafting are the better options, simply because they are the most flexible in their bonus (BS can gem extra PvP Power/Resilience and both can gem extra secondary stats).
If we're talking open world or regular BGs then Engineering is the best way to go.