It depends - if you are running IHG's promo, then it might be a good idea to move over and score some points and status. E.g. Mr. is running for set your sight promo - all he needs is a total of 5 nights, 2 hotels have to be outside Sweden (piece of cake as there are no IHG hotels in Sweden), 2 CP, 2 HIX, and 1 night on HI. After 5 nights he will score a total of 50k IHG points. Marriott's megabonus - well I have to stay 15 nights to get 25k points - what can you book for 25k points in Hong Kong/Berlin/London/Vegas? 1 hotel in the middle of somewhere of nowhere.

That 50k points = 10 nights PB stay!

I found IHG upgrade ratio being higher than Marriott (both Plat). IHG points in general are not as good as Marriott points - but with a few exceptions in Hong Kong/Germany:

IC Hong Kong - 35k IHG points/ JW HK Cat 9 (45k?)
CP Kowloon East - 20k/night with free Plat Brekkie/CY Sha Tin - going to be cat 4 which requires the same number of points - worse location
HI Berlin West - 15k points - try to redeem any Marriott hotel in Berlin, you'll know what I mean

Another killer for IHG - Point breaks. I don't use it all the time, but when I do they are super value for money - 5k points/night ($35) is unbeatable.