This is really late but thought I'd post a review for regular Uber service that I took on a Friday at 5:30 PM in April so that there's more info for this thread on the options.
I signed up for Uber on that day and requested a Uber black car from Madison Ave and 57th to LGA (Delta Terminal C). Being in the heart of Midtown, there were numerous black cars available but somehow a Cadillac Escalade answered the call (my wife was pleased).
It was at the corner within a few minutes and it took me longer to get to the car from my office than it did for the driver to arrive.
Anyway, we took the Queensborough bridge and took surface streets and the GCP to LGA. It was fast... 7.9 miles in 31 minutes and 58 seconds. The driver was excellent, the Escalade was clean, and it was smooth sailing. Cost was $46.28 but Uber rounded that down to an all-in cost of $46, which includes tip. As a first time user, I also got $10 off.
Definitely a great way to get from midtown to LGA as taxis are usually in the $30s with the traffic.