What keyboard are you putting them into? If you're putting them into a hotswap board it's not terribly difficult to swap out springs after the fact.
I would personally recommend starting with the 62g. The Boba U4's have a big tactile bump so they feel heavier for a given spring weight. The difference the 62g and 68g isn't huge anyways.
If you find that you're bottoming out very hard, then consider a heavier spring. I posted in another thread that people that prefer lighter springs tend to find that they type faster on lighter springs, or don't mind (or even enjoy) bottoming out, or find typing on heavy springs fatiguing and tiring. People that type on heavier springs often type harder naturally and want to avoid a harsh bottom out (or avoid bottoming out entirely), or may find that they type faster on heavier springs because they "boost' you on the return stroke. However, Boba U4's are difficult not to bottom out in because of how large and spread out its tactile bump is no matter how heavy the spring is, and I've tried 90g springs in them and still end up bottoming out, so the main advantages of having a heavier spring are lost. It also has rubber dampeners so the bottom out isn't that harsh.
