There's no easy answer to that. Depends on your stay patterns.

You could theoretically apply separately for the new card rather than converting and get a higher bonus, but it may come with minimum spend, and that's a new inquiry/new account on your credit report.
If you don't spend a lot on the card regularly 50,000 points sounds easy. If you are clearing a lot of spend, you have to weigh the loss of the travel insurance benefit and 1 elite night per $3,000 in spend moving across the card against the slightly higher earn rate on everyday purchases, 1 extra point per dollar on marriott purchases, and the certificate being good for up to 35K point redemption rather than a 25K one on the old card.

With my current patterns (0-20% travel per month, old lifetime plat/new lifetime premier plat, not moving much if any spend on the card right now) I'd convert for 50K points. This is an individual consideration though, I don't need to chase nights anymore to re-qualify for current status or to qualify for any higher lifetime tier.