SPG are more valuable per point, but the downside is you can only earn 1x, so cards that offer category bonuses are often better. Methinks you'd likely get more value with the Marriott card as you'll get 5x when spending at Marriott.

For example, $10K spend at Marriott would only get you 10K SPG, while you'd get 50K Marriott. Then compare what sort of value 10K SPG would get you vs 50K Marriott and you can quickly decide which program is better for you (my bet it's Marriott)

But why just get one or the other? Apply for a bunch of cards, even if only to get the sign up bonuses.