A quick overview, from “30,000” feet:
Vex and FTC are roughly identical - ‘roughly’ - and I’m sure there will be plenty of commentary to follow that will tell you all about the rough spots.
They are comparable in cost and in the market that is targeted.
As I’m sure you know, FIRST has JrFLL, FLL, FTC, and FRC. Prior to FTC was VEX. For reasons outside the scope of this thread a decision was made to close VEX and start FTC. Ultimately a group of people negotiated the rights to take VEX outside of FIRST and start an independent organization.
Today, VEX and FTC compete in roughly the same market.
Some students progress through FLL, FTC, FRC.
Some students progress through FLL, VEX, FRC. Some just do VEX, or FRC, or FLL, and many other combinations.
Some students do VEX and FTC. It isn’t uncommon to see teams at both VEX and FIRST competitions.
While VEX and FTC compete in the marketplace, it is a friendly marketplace.
Did you know that some of the top people of VEX, including the company president and the head of engineering are big time mentors with well known FRC teams.
Did you know that the VEX and FTC competition court is physically essentially the same.
There are a lot of reasons people pick VEX versus FTC. I would do a straight hard nosed examination of the programs and pick what is best for you are trying to accomplish. You need to consider whether you are doing this as an in-class curriculum or an after school activity. Do you want to maintain a progression in programming familiarity, going from FLL to FTC NXT bricks? Just to fuzzy things up there, you can do RobotC and Labview on bot the FTC and Vex system. You can get curriculum and classroom packages from VEX, and so on and so forth.
Do not worry about the VEX camp versus FIRST camp issues. It is a huge marketplace. It is only about 4% penetrated. There is room for everyone. And competition is good for the consumer.