If you had to choose, despite both options seeming bad, which would you choose?

The biggest problem with this question is the part that says, "if you HAD to choose".

You never have to choose either of those losing moves. If you ever believe that you DO have to choose, then honest to God, it really makes no difference. That sort of person would be a degenerate gambler who would still lose the money even if that bet won. Honest to God, it just makes no difference for anyone who says they HAVE to choose between bets like that.

Play black.

Why? If I'm comfortable betting a certain amount of money on a hand, why would I want to raise that bet 5 times on a hand of blackjack? Then I might have to split and/or double down and be betting a lot more than I like.

Betting on black after 5 reds hit? So what? That's just a normal regular bet. Did you mean to suggest a 5x wager on roulette as well? 5 reds doesn't mean anything. Losing 5 blackjack hands in a row might mean the count is against you (but I don't count).. even if you did mean a 5x wager on black, I'd choose that one. No chance to lose more.

The first option you mentioned in the Martingale system. It has been discredited as a viable betting system many times over.

Therefore I would choose the latter. At least the black or red bet has just under a 50% of winning.