Variants:
5/off - rips off a checker, leaves no bad numbers next turn, reasonable distribution, does not prepare the back point for removing
6/1 - leaves a good distribution, leaves bad 63, prepares the back point for removing, puts a checker on 1pt
6/2 5/4 - prepares the back point for removing, puts a checker on 2pt, leaves bad 63, 66, 55

What is the best?

I'd look for the safest play, since gammons are almost sure if we're not hit.

5/off looks safe, but its short-term safety. You will often move both spares deep next roll, leaving 3 stripped points, which can generate troubles down the road. Reject.

I'd prepare to clear the 6pt. with either 6/1 or 6/2 5/4.

The 5pt. stack after 6/1 isn't problematic, since you won't be playing 2s with those spares, but rather clear the 6.

6/2 5/4 seems more risky short-term, but gives nice wave-shaped spare distribution. You often want that in bear off vs anchor. It's one of the most usable rule-of-thumb advice I've read in the books (don't remember which one, but I think it was Bill's "Modern Backgammon"). It points to the best play suprisingly often.

Not sure what I'd choose in the end, but probably trust the "wave" rule once again, like I've used to, and go with 6/2 5/4.

I'd also play 6/2 5/4. My rule for bearoff positions where safety is the only concern is "avoid the pseudo-gap".

A pseudo-gap doesn't refer to an actual open point, but rather a gap in the distribution of spares. In the original position, Black has spares on the 6-point and 5-point, but no spare on the 4-point. Hence the pseudo-gap. Playing 6/2 5/4 fills that gap and should leave a slightly safer bearoff.

It's true that 6/2 5/4 leaves a few shot numbers next turn, but that's always the case as you get ready to clear a point.

5/off leaves one blot number next roll (33). So it's pretty clear to me you're safer long term paying two blot numbers with 6/1 because you get to clear the 6 point a lot next roll which you don't with 5/off. If you play 5/off you just end up paying those two (at least) blot numbers later usually.

Not sure between 6/1 and 6/2 5/4, it's possible it's safer long term to play 6/2 5/4 due to the smoothness of the position even though 66 and 55 leave a shot in addition to 63.