The vans aren't horrible. I don't like waiting until they fill up, but then it's usually not so long. It's just that after I have driven to Lubbock, flown to Houston, rushed to my connection, flown to Cozumel, waited for the slow people in front on me on the plane to get off so that I can, hiked to I&C, spend an hour in Immigration line, grab my bags, clear Customs (Cancun furnishes free carts; why doesn't Coz?!), grabbed a ticket, loaded onto the van - I'm ready to go, tired of waiting in lines.
You do need to be careful with your bags, as the driver can't memorize exactly which ones belong to whom - trip after trip. He'll unload whichever he is told at each stop, but there could be miscommunications. I never thought of writing the van number down, but good idea. I get out at each stop to make sure my bags don't get off early.
One time the driver passed my hotel to drop a couple off at their further hotel, then doubled back to drop me. Maybe they bribed him, or maybe it was easier for him not having to cross traffic every time with left turns in and out? I really need to see if Walmart sells patience before I leave.
And traveling solo like I usually do, a van ticket is cheaper than a taxi.