Many teams have a “default” drivetrain style that they use most years, while staying open to changes depending on the game and field. For my current team, I’d say it’s a 6 wheel West Coast drivetrain with 4" grip wheels and a drop-center. This year we deviated from that in some ways, and hopefully I can give some insight into our design process:
-Last year we had mild trouble with the endgame platform, and got high-centered a couple times. This year had a similar endgame platform, so we decided to use 6" wheels instead of 4". We figured 6" wheels would help a little if we tried to climb to Level 2 or 3 as well - to drive onto a platform you have to get the center of your wheels above the surface of the platform, and starting with the center of our wheels an inch higher is one fewer inch we need to elevate the bot. The tradeoff is moving our center of mass ~1" up, which we decided we were okay with.
-We wanted more maneuverability than we had last year, and considered doing a drivetrain with side-movement (H-drive, swerve drive, etc). But the tradeoff with those would be more time needed to program them (and thus less driver practice time), and they would take up more space on the base of the robot where we wanted to put electronics and other mechanisms. As a compromise, we decided to put omnis on the front and back, and have only the middle two wheels be grip wheels. This also made the drop-center unnecessary, as the omnis allow us to turn well without it. Keeping grip-wheels in the center made us a little more resistant to being pushed around than we would have been with all omnis.
-We considered using pneumatic wheels instead of grip wheels to help us survive driving off Hab 2 at the start of the match, but ended up not doing it. Towards the beginning we were thinking we’d have a good autonomous mode and starting on Level 2 would mess it up because we wouldn’t know where we landed/what direction we were facing. We didn’t consider starting on Level 2 until we got to our first regional and didn’t have working auton, and at that point we didn’t want to make big, untested changes to our drivetrain
-We ended up playing defense for a good chunk of our first regional and turned out to be really good at it. Between the two regionals we debated swapping our omnis for grip wheels to give us more traction for pushing opponents. But because we hadn’t designed a drop-center, we wouldn’t be able to turn well at all with all grip wheels, and we decided the dexterity of the omnis would serve us better than all grip with no drop-center
These decisions all started from the premise “if you want to deviate from [default drivetrain], you need to have a good reason” and I think that’s a good way to approach it if (like us) you want to get the drivetrain designed and built quickly so you can move on to more interesting parts of the build. If your team finds drivetrains really interesting and wants to invest more time in developing an optimal one or a cool one, maybe a more “blue sky” approach would serve you better.