Speaking from a personal opinion, I prefer Lethality > Concealment. Concealment plays somewhat similar to Deception but with even fewer buttons and nothing that lights up and screams "BAM PRESS ME".
The glory is you can play both with the same armor set, stats, and amplifiers and they perform pretty much the same in a dummy parse. Without knowing exactly what type of content you are looking at, it is hard to refer one spec over the other.
For instance this is my stat/gear spread on mine. It is by no means perfect, but managed to pull 21k dps as both specs, which is more than enough for most content in the game.
Scoundrel - 5-4-2020
6/6 Tacticians
8.40% Tech Wizardry
2.20% Periodic Intensity
Mastery - 12,117
Endurance - 16,588
Power - 9,386
Crit - 3,193
Alacrity - 1,290
Accuracy - 1,681
Scrapper Parse - 21,232 DPS - http://parsely.io/parser/view/495560
Ruffian Parse - 21,152 DPS - http://parsely.io/parser/view/495091