It all depends on the speed of the internet that is feeding the WiFi. I'm guessing your 4G is going to be much faster than most public free WiFi hotspots, probably a lot faster. My WiFi at home is faster than my 4G but out in public, i'd probably go with 4G if you are looking for speed. I think the wifi will use a little less battery power on your phone though.
I don't know much about Android, as my name suggests, but I do know some things. You can't make a blanket apples to apples comparison between WiFi and 4G, because it depends on a couple of things, mostly Location Location Location, and you probably won't get the same results twice.
WiFi is a wireless connection to the Internet through your ISP provider, and currently there are three flavors out there, generally referred to 11b, 11g, or 11n. (these are really IEEE 802.11b, g, or n specifications), and it comes into play in the wireless router that provides the connection. You mostly see it in the speed (11b is the slowest and 11n the fastest. but there are some other factors in the protocol, including the encryption used between your wireless device and the router. Older devices, like my old laptop, only can use the 11b spec. My current laptop can use 11g or 11n. My Wii can only talk 11g. The TB can use all 3. So, regardless of how fast your wireless device is, in this case a TB, it can't access the Internet any faster than the WiFi router will allow. Your not likely to find many public WiFi locations with routers that support 11n. Once you get past the router, than you have to deal with congestion on the backbone in your immediate vicinity. Some days my Comcast connection flies, and other days it just drags. Just depends on what everyone else in the neighborhood is doing at that time.
If you look at the phone side of things, its always trying to maintain connection to a cell tower, but other towers in the immediate vicinity know about you. If you happen to live or work in a location that is near the overlap of two towers, moving from one side of the building to the others could trigger the change from one tower to another. You might see this as a momentary loss of connection, or a change in the signal strength.
So, the throughput you get today (upload and download speeds) could be different tomorrow, and what's faster on WiFi today might not be tomorrow.
WiFi, however, should be much easier on your battery, since the phone doesn't have to transmit as far as it does to a cell tower, assuming that you don't have one in your backyard.
Three other things to consider. First, LTE is new technology, and I have to assume that Verizon doesn't have all of the bugs out of it yet. I believe that they are still tweaking settings just as we are on our phones. Remember, this is the 1st LTE phone, and their only experience prior to the TB launch was mobile broadband for laptops.
Second, everyone has gotten used to everything working perfectly, like their old landline phone. About the only thing that could knock that out was physically cutting the wires. However, cellular networks, especially since the addition of data transport, have gotten exponentially more complicated, and their failure rate is grown exponentially with it. I don't know how common it is, but I expect that Verizon experiences the same kinds of equipment failures as the rest of the computer industry. Some failures may reduce capacity, and some, like a power failure, could knock out the whole tower. If you are not in an area with a lot of cell towers, reaching out to the next closest one could tax your connection. The bottom line here is that some of the intemittent problems being reported could be related to Verizon network issues, and we'd never know.
Third, upload and download speeds were generated in a lab under ideal circumstances. Just like automobile gas mileage figures, they have no basis in reality. They do give you a feel how the device compares to other devices, but experiencing those speeds in real life, especially sustained over days or even hours is just not going to happen