You might want to check into additional costs (since you're only Silver) of things you might use, like internet and breakfast and parking. If those are much higher at one of the hotels than the other, that could be another factor.

If all is really equal, I'd stay the difference in value between Hilton and Marriott points is not great enough to necessarily cover the difference between 40k and 25k. So on purely that aspect, I'd say the Marriot 25k is a better value than the Hilton 40k.

(You might want to check whether Hilton has a cash+points rate there, though. That could cut the points in half to 20k, perhaps, while adding only a relatively small $$ cash component. And if you book by tomorrow (Jan 31) after having registered for the Get Points Back promo (or it's called something similar), then you'd get 33% of your points back after the stay. (But that promo only applies to cash + points, not regular points-only reservations.)

But all is often not equal. How do you replenish these points? If it's much easier for you to replenish one or the other, that could alter the balance of value for you.