For data, you probably know about what LTE/4G brings. From a 3G standpoint, Verizon is entirely EVDO rev A which means peak theoretical rates of 3.1Mbps down. I typically see between 1-2Mbps down (sometimes higher) and 500-900kbps up. I've found this to be pretty reliable in my area. All Verizon towers nationwide will be EVDO-capable so 2G isn't an issue in Verizon's coverage area (unlike AT&T where a large portion of their footprint is EDGE). When you do drop to 2G, it's in the event of being on the outer fringe of a coverage area OR more rarely in a situation where maybe the EVDO signal is weaker. Verizon's 2G is known as RTT which is pretty slow. The entire voice network is operating on RTT (this is what makes voice coverage robust) but it is capable of handling data operations in the absence of an EVDO signal (albeit with much lower data rates).
Verizon's implementation of LTE is pretty exciting since it'll be a marriage of the best of both worlds. I like the ideas of HSPA which was a huge improvement on the GSM standard, but it still doesn't touch CDMA for coverage and load handling.