The ProTips seem to recommend Transit VPC, but I would have thought Transit Gateway is today’s solution of choice?
This question has come up before here in the forum. Basically the difference is that a transit VPC is more of a network architecture concept while Transit Gateway is a service. Gateways can simplify your network but there are some reasons why a more traditional transit VPC. For example, some people don’t like the fact that a Transit Gateway is kind of a black box.
AWS will be the first to say there is no "best" way because of so many different variables. (See AWS Transit Gateway Tech Talk: https://www.youtube.com/watch?v=A_2qq9fFxVU). For the exam, it’s important to know the general use cases where a Transit VPC or a Transit Gateway might be used but I wouldn’t worry about which is "right".