It will depend on what will fit you as well as the bike.
To find the biggest travel dropper you will need to carefully check the measurements for maximum insertion depth, overall length and stack height. The easiest way would be comparing current fitted seatpost measurements against the One Up dropper post.
You just need to make sure if you need to fully insert the bottom section into the seat tube the top section is not taller than you need to ride comfortably when fully extended.
Because it is a One Up if the stack height is just over what you need you can shim the extension (stack) height down by 10 or 20mm for an ideal fit.
Max Insertion Depth for the SC Hightower directly from SC support:
On my Hightower V2 XL, the Oneup 210 has a total insertion depth of 297, the actuator is 15mm, so 282 without actuator. I found the 210 can drop all the way and still work normally on my XL bike, however I am too tall to slam the post to the seat collar, I would need a ~250mm dropper as I like XC height when the lands are flat.
I'm just guessing as I don't own a Hightower but suppose that will be for a seatpost/frame design reason that may or may not be visible from the outside or maybe an internally routed cable exit point? 🤔 Hopefully someone will know for sure and can give you a more definite reason.
So just posting here for reference, in the future, if someone is interested.
I took the dropper seatpost out, placed a big flashlight in front of it and saw that there's a small bump in the frame. The exact bump depth is 350mm, meaning - that's the maximum insert (minus few mm).
I made my mind to take a PNW dropper instead (30% less and offers more of less the same experience.) - I'll update here how the 170MM PNW works and if I need to reshim it.
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