Although it sounds very obvious, this can be tricky decision. 4G is definitely faster then 3G and 2G speed, but the bad news is that 4G service is not yet distributed as widely as their predecessors. 4G is just getting deployed in the cities and densely populated places first and yet to get deployed in less denser areas. A future 4G service in a given area is a open ended promise that the cell phone companies cant possibly put a date on.
The cell phone booster systems for 4G is a newer technology and as of now a system that works for 2G, 3G and 4G is made for large coverage areas, in the upwards of 30,000 Sq ft and above. If you do not have such a requirement, then it is advisable to choose 3G booster system and upgrade to a 4G compatible at a later point of time when the 4G service is more wide spread. It should also be noted that the internal and external antennas that we provide with our 3G booster systems are also compatible with 4G frequency. So, the only item you may have to upgrade is a 4G amplifier, specific to your carrier such as LTE in case of Verizon and AWS in case of T-Mobile
Secondly, since the technology is recent for 4G, its worth a wait for the manufacturing cost to go down and more suitable for home application.