Here's the master thread about the traffic debacle at LGA.
https://www.flyertalk.com/forum/new-...i-pickups.html
Construction is ongoing and it can still get very backed up at peak periods, but other times it can be fine. Delta uses terminals C and D. There's a new concourse that opened recently in terminal D, but it's not a "new terminal."
A 10pm-12am arrival midweek is probably okay, except maybe Thursday night, lots of consultants returning home. That's probably too late for the "taxi-like" lines for Uber/Lyft which I think are more efficient than waiting for your assigned driver, although I don't have experience with the taxi-like lines:
Lyft trials taxi-like lines at airports
https://www.flyertalk.com/forum/new-...l#post31327503
Taxis will require an off-site shuttle bus, so I wouldn't do that unless there's a real cluster with the car services.
Here's the old Wiki on the various transportation options, and pros/cons, which generally still holds:
https://web.archive.org/web/20160419...9_to_Manhattan.
In terms of your departure, a 6-7pm flight will likely involve peak traffic, probably worst on Thurs/Fri. Taxi/car service into LGA is best as the bus has to circle around through terminal B first which will waste a lot of time. I might consider 7/E/F subway to Jackson Heights and taxi from there since you'll be trying to leave Manhattan at rush hour. I'd probably depart Manhattan no less than 2 hours before your flight, more if you're taking a car from midtown west or are checking a bag.