For my favorite title Legion of Superheroes, I would reboot it by combining aspects of all the previous reboots into one. They would have a really huge membership with a primary core cast being focussed on from story to story. They would be aware that their history is all messed up due to the Time Trapper's manipulations but there wouldn't be anything they could do about it other than preserving what they had now. The title would not be held accountable for the ongoing changes for the present day DCU. Superboy would be the one from the silver age. Maybe he would be from an alternate universe or be part of some chronal destabalization by the Time Trapper, whatever. With that in place they could just go on and have adventures using the futuristic backdrop that helps make the Legion unigue.
They would also age in real time as much as possible. That would force change and growth without having to do another reboot IMHO.
