Megabus

Boarding location for the Memphis stop is on Shadyac Ave & 2^nd. There’s a MegaBus sign on Shadyac ave. It’s near the entrance to the parking lot. Megabus staff at this location were both professional and nice. Your luggage may be subject to a weight check, make sure you’re under 50#. Yes, they’ll pull out a portable scale. I advise you to arrive at least 30 minutes before your trip. It appears to be a busy stop.
Tip #1: Download the Megabus App and check prior to your trip. You want to confirm your bus time, so do this a few hours before your trip. It’s a free app and simple to use.
Tip#2: I had a layover in Memphis for 4 hours and wanted to grab drinks and food. I took the trolley to the downtown/​business district. It’s about a 5 minute ride and I was in the lobby of a hotel having drinks and a bite to eat. $ 1 cash each way. There’s also a nice public park off the trolley line. Trolleys run roughly every 13 minutes and the staff were very helpful. You can grab snacks and coffee at the Shell near the transportation center if you don’t feel comfortable taking the trolley downtown or pressed for time.
Tip #3: There is a public bathroom at the transportation center. Not the cleanest.

Now, I can’t speak for every different journey that they have available, but my trip from Memphis to St Louis and back was pretty fantastic for a bus.
The pick-​up in Memphis is at the MATA terminal downtown… but along the side road and not actually under the awnings.
The buses themselves were nice. You have free wifi, albeit slow wifi, outlets to charge your electronics, and decently comfortable seating. I think I got lucky in that my trips weren’t heavily traveled… so I got a row to myself. Had there been more passengers, it definitely would have been uncomfortable, as the seats are pretty close together.
I was impressed with the cleanliness of the bus itself and the overall efficiency of the staff. Plus my round trip from MEM to STL and back was only $ 65 at the last minute… I understand it is even less expensive the further in advance you book. Definitely going to be a first choice of mine for road trips, cause I don’t like to drive all the time ;)