Each has its advantages and disadvantages. First, FDD wastes frequency bands. In fact, TDD will not be much better. Although there are many uplink and downlink ratios, the actual use will be fixed (at least TD-LTE, which is easy to understand. Different base stations must be synchronized. When one base station goes up, the other will interfere with each other too much), that is to say, it will be overloaded while it is empty. I'm not familiar with FDD, but it seems that 1: 1 does not have to be allocated up and down, so TDD has this advantage in theory, but it is actually very small.
In addition, TDD signaling overhead will be a little more, of course, the advantage is that more users can be supported when the channel conditions are good. Generally, it won't be too bad. Driving at high speed? I think what you said is about the same.
Personally optimistic about FDD, which is the mainstream technology in Europe and America. 3GPP LTE-FDD and IEEE 802. 16 are FDD, and TDD is made in our country because we don't want to pay patent fees. It is also said that TD and FD of 3GPP are integrated in the research and development of the next generation protocol.