In general, I'd always advertise the Old-Formats version, because it includes the levels as intended, but in your case, I think you're already past all the major noteworthy radiation- and slowfreeze levels (like "Ayo Technology", "Japan", and "Only time"). After a quick look, there should only be a single one remaining on the Legend rank ("Blowing in the wind"), and two on the Groupie rank ("All you zombies" and "Hiroshima"). Meanwhile, the New-Formats version doesn't crash due to graphic-set mixing, which is a huge mark in its favour, considering overall game stability.
So maybe, whenever you decide to continue LWT, it's best to do so in New Formats, and then only switch back to Old Formats for these three select levels?
Or playing them in New Formats first, just like any other level, and then showing the Old-Formats version for comparision.
Of course, continuing in the Old-Formats version would also be perfectly fine, since I'll continue to maintain both versions; any backroute fixes will be done in Old Formats first, and the level will then be re-converted to New Formats by opening it in the new editor.
And you actually haven't had nearly as many graphic-set-based crashes as I would have expected, so the Old-Formats version still seems to be quite stable on your computer as well.