Depends what you value. Earnings-wise, it is generally far easier to accrue points with PC, even without the 'stay twice, get a free night' promos that have run for the last 2 years. 2 nights at your local $50 HIX for a free night at a top IC is an outstanding deal. PC also has a far bigger range of properties in much of the world, especially Europe, and has the easiest attainable top tier.

The downsides are that benefits are often minimal, even for Plats.

Ambassador is actually a good investment of $200 if you stay at IC's, because the benefits are guaranteed - 4pm check out, guaranteed upgrade, free pay TV.