I have been IHG platinum for a while (actually since the Hhorrors devaluation) and got re-qualified for 2015 at about June (and likely for 2016, since I got 95 nights), and being Marriott Gold via UA, I am giving it a try this half of the year and have about 12 stays at different Marriott Chain hotels. Here is my comparison of the frequent guest programs:

-Earning potential: Pretty close. Both programs have promotions, even though IHG's tend to be a bit better. Unfortunate 5 points/$ for suite hotels with kitchenettes for both places

-Redeeming potential: IHG, hands down. Same earning potential, but hard to find Marriott properties for under 15K points a night, where there are lots of IHG properties at the 10K a night level plus several at the 5K level (at least where I am interested in going; YMMV)

- Elite qualification: IHG hands down. Rollover nights plus Platinum at 50 nights or 40 nights and 4 different brands or just by getting the credit card. Reward nights count towards qualification also.

- Elite benefits: Marriott maybe because of the free breakfast (other than Courtyard), but I got upgraded only once in 12 stays, where I rarely don't get upgraded at IHG properties. Plus no elite benefits at InterContinentals is somewhat of an issue.

- Properties: Marriott hands down both in number and variety. I have stayed at RI, SS, CY and Marriotts and, other than Courtyard, which I really do not like for a few reasons, the Marriott properties are better than most comparable IHG properties. RI is better than Staybridge by far and SS is better than HIE. One slight issue is that they are somewhat cookie cutter, where Holiday Inns and Crown Plazas usually have their own individual character. Another issue is cost. IHG Full Service hotels are less expensive than the Marriott counterparts (I do not consider CY full service, because of its limitedness and lack of room service.) Residence Inns are becoming one of my favorite chains...

-Customer Service (of Frequent Guest program) and web site: Marriott by much.

I will keep staying at Marriotts until the end of the year and will return to IHG next year. The redemption is a big thing for me... If someone does not care about that, I'd say that Marriott has its benefits.