Starting from scratch, I'd probably diversify to HH. For one, with their Surpass card, you're Gold out of the chute and if you're willing to stop using your SPG Amex for a bit, you could hit Diamond on card spend alone ($40k per calendar year).

The big benefit to Marriott comes when you hit the Travel Package level - giving you a 1-week stay plus the best "convert-out" option in the industry. But to do that, you'd have to actually make it your primary stay chain and do a year or two worth of Plat-level stays. There aren't many good "convert in" options to Marriott, whereas HH has a very good one from AA.

(In other words, if you choose, your Marriott Travel Package can become 1 Marriott week plus 1 Hilton week plus some AA miles leftover... )

So it all depends on how much real stay activity you want to move. If you want to stay mainly Starwood but quickly build a balance and a midtier status for backup purposes, just switch spending to the new HH Amex. (There are "good value" HH redemptions in the 4-night AXON award, so if you like shorter stays this is an advantage over Marriott.) If you really want to switch primary stay behavior, call Marriott for a status challenge, get their newest MR Visa product, and start working your way towards your Travel Package.