I've worked center, VFR tower and a TRACON. Each one provided training that made me the controller I am today. Each one also had hours of mundane broken up by moments of sheer terror! (What a blast!)
Currently, the FAA is scrambling to come up with numbers of controllers, so in my humble opinion, they will continue to split TRACONs from the towers, and then contract out the less busy towers. This will allow them to show greater numbers at the approach controls which they will combine with bigger facilities or centers. This will reduce their overhead,(less buildings to maintain) reduce the number of positions to staff, and show how they saved tons of money by contracting out the towers to private companies (look how well that worked with FSS). My advice would be to pick a 7 or 8 facility, check out, then move up. I realize that your question dealt more with 'which one would be better'. That's a personal assessment that only you can answer. If you like seeing sunrises or sunsets, center or straight approach controls ISN'T the way to go. If you don't want to talk to vehicles and the occasional monkey that drives them, towers should be last on the list!
Hey 'Almostretiredatc', congrats on the date and thank you for the service to your country. I have 3 years, 10 months and 12 days, give or take.
It is truly amazing how much ATC experience is walking out the door on the FAA...