I haven't played an Operative yet, but I'm pretty confident both share minimal similarities.
I wouldn't say one or the other is superior per se, merely that I've had significantly more success using a lethality build, in both PvE and PvP.
Certainly, I had difficulties with a Lethality build in the earlier levels, so I respecced into Engineering, and at 45, I embraced Lethality again, with significantly better results. The people who say Cull is required to make Lethality good are definitely educated in saying so. I would wait until your 40 (or even 45) before attempting a lethality build.
As for PvP, my opinions are probably different than most. I see a lot of people claiming to make use of cover as a lethality specced sniper, and while I won't criticize the choice, I don't think it's the best way to optimize using a Lethality spec. The majority, if not all of your cover dependent abilities don't complement any of your Lethality centric/specific abilities at all. So you'd basically be using cover strictly for the defensive buff, which in my experience, are negligible in PvP (at least, if you're specced into lethality).
In Short? I don't advise using Cover at all in PvP as a lethality sniper, so I definitely recommend against grabbing any skills in the other talent trees that complement/require cover, such as Cover Screen/Ballistic Dampers.