Round trip bus ride from Mazatlan to Zihuatanejo Help

My wife and I have taken the bus the past 2 years in Feb. from Maz to Zihua. Never RT, however. Here's what I can tell you:

Both trips were fantastic. On one bus each seat had an individual monitor to watch a choice of movies, do internet, etc. All had wi-fi. All very comfortable. Way more comfy than a main cabin airplane seat and never crowded. Some of the buses had only 15 seats. We also always bring 2 huge suitcases each--no problem, no fees. Both trips the bus went through and stopped for short times in Guad, Morelia, Uruapan and Lázaro.

2013: Maz--Guad-->Primera Plus---leaves from its own station, not the main downtown Centro de Autobuses. 440p 1W. Departs at around 10a and gets in about 6ish.
Guad--Zihua-->Estrella Blanca [Futura] had a couple hour layover in the bus station and had to transfer to another terminal. Overnight arriving about 5:30-6a. 560p 1W
2014: Estrella Blanca entire way. I think this bus actually originated in Tijuana. We departed Maz around 10 or 11a from Centro de Autobuses and arrived in Guad about 7 or 8. Had a 30 min layover and continued on the same bus to Zihua arriving 6 or 6:30ish. 19 hr+ but great. 1100p 1W.

We got help making our reservations in 2013. The internet sites for some of the lines were not so good. 2014 that changed and it was easy to see which lines went where and to make reservations. On most you can click and choose your seat, as well. One can also go directly to the bus station and make reservations.