I picked Marriott because I'm based in Europe and Marriott has a good coverage of mid-range hotels in Europe. I'm also with IHG but I only use points for their PB offers because I think the whole IHG company is a mess.

I like Marriott because the hotels are consistent (you know what to expect - nothing exceptional but everything you can expect). If there is any problem with your stay you can escalate to higher level easily and Marriott does take the issues seriously and do the right thing.

I like the lounge access and the promo (stays 2 times get a cat 1-4 night). Yes it's not as awesome as Hilton's but I have a good way of using them.