Low but safe for now -- is that good enough?

I think it's clear that I must take his 18-sided die -- but does it make more sense to
take it with my 6-,20-,and X9- dice, thus rerolling the very low 20-sided die [but leaving
my own 18-sided die to be taken in a skill attack that will reroll HIS 20 sided die] -- or should I reroll the 18-sided die, leaving the 20-sided die quite low (but safe for the next turn, since he has no way to take a die with value 7 at the moment.] and risk him being able to reroll his 20 sided die to be the largest die on the board?

Button Men Game #684849
This game is 'for fun' and does not count for player rankings.
Arena Game: Random TL BM from 2002 Rare-Promo

Skills in this game: X Swing
Player: ElihuRoot *Dead Dude* *Fanatic*
Your Button Man: MAX(p) (4 6 18 20 X) Score: 28.5 (1 sides) Rounds Won/Lost/Tied: 1 / 0 / 0 (Out of 3 wins)
Your Captured Dice: None

4-sided die	6-sided die	18-sided die	20-sided die	X Swing (with 9 sides)
1	6	13	7	4
4-sided die	6-sided die	18-sided die	20-sided die	X Swing (with 6 sides)
4	5	17	4	4

Opponent: SliderDF *slider*
Button Man: MAX(p) (4 6 18 20 X) Score: 27 (-1 sides) Rounds Won/Lost/Tied: 0 / 1 / 0
Captured Dice: None