Guild Wars 2

What do you think are the best traits for solo dungeons like arah with engi?

I like 6/4/0/4/0 for solo. With the pistol/shield over the blind, reflect and additional blast.

some people will tell you to run the meta, which is 6/6/0/0/2. however, I personally never run the meta because I hate grenades. Besides, bombs offer better personal dps, which means bombs are better for solo (at least for most stuff – might wanna stick with grenades if you fight Melandru’s priest in Arah p4).
My default setup is 5/5/4/0/0, focusing bombs and rifle (steel-packed powder is still useful because fire bomb stacks vuln multiple times). I prefer the quality of life that power shoes provides over having to swap to speedy kits between fights. Also, if you aren’t focusing full dps skills (including toolbelt skills), I think energized armor might be better than static discharge – most toolbelt skills don’t do anywhere near as much damage as bomb aa (in some cases, even combined with static discharge damage. multi-target hit isn’t much of a bonus to static discharge because bombs can hit more targets than static discharge.)
All that being said, I do often swap traits according to the situation, especially solo because I have nobody waiting on me. For example, at Belka in Arah p2, I run healing traits x/x/6/4/0 (x = one of those is 4 the other is 0, I’m still experimenting whether power and +10% bomb damage or precision and rifle traits are better) because I refuse to do the ooc exploit, and also don’t wanna resort to hiding to heal (hiding is an acceptable way to fight her, just not my style. exploiting is not acceptable. neither are worth recording in my opinion). I definitely recommend retraiting for a legit Lupi fight – at least get invigorating speed (I currently use adrenal implant and fortified turrets instead, but might tweak my solo build soon).

tldr: focus on bomb kit traits for most stuff, but tweak your build according to the situation – nobody is waiting on you to decide on traits when you solo.