I'll tell you my experience on both:
LaMarzocco 4 group: It was an older 4 group semi-auto Strada, only 3 groups worked, not one brewed the same. Needed major work, but it got the job done for the boss.
Coolest thing was the LaMarzocco grinder: You had to insert the portafilter, it portioned, ground, and tamped for you. Was good for hi-volume. The 2 locations did about $15K/day
Astra 2 group: It was a new machine with the SUPER LONG steamwands. Mega-bonus for when you gotta make 4 lattes or more in the 64oz frothing pitcher. Nice was the manual control switches to turn on and turn off the pump, for every shot. Your coffee is constantly changing with humidity/temperature of the environment you are in and it was nice to have total control on the brew cycle for every shot. Brand new, never had a hiccup, beautiful.
Mazzer grinders: These were digitally adjustable for the dosage. These babies were Doserless, and doserless is the way, always fresh, every time, directly to the portafilter. No coffee should be ground and waiting for customers, if you truely want the best
Do your homework: Visit and try as many machines as possible at all the coffee shops you can, talk to the baristas. Let them know you're gonna open a cafe and you'd like an opportunity to try out the machine. Get feedback, especially from the experienced ones. Good luck.