I'm a former Amex Platinum cardholder and a current Citi Chairman cardholder (though I hold several other Amexes that I use for most of my spend.)

The Small Business version of the Amex Platinum costs $300/yr, vs $395/yr for the personal version. The benefits are almost the same, but you do not get the everyday double points on the Small Business version (this can be fixed by, say, getting a personal Blue.) You also get some OPEN discounts with various merchants. One can apply for the Small Business version as a sole proprietor using his or her SSN in place of the EIN if desired.

According to posts in the American Express forum, this benefit is indeed officially being phased out, if it has not already been.

I have noted that the Amex website is often very slow and spits out errors more than it should. Additionally, the last several times I have tried to use the Membership Rewards website to redeem MR points, at the final stage the transaction (a transfer to Delta in each case) failed, forcing me to call to make the transfer. Nonetheless, I agree with your other points and that the website for the Platinum card is indeed superior (if slightly broken at times.)

This is actually the ONE benefit that the Business Platinum seems to lack; you have to call them. However, one can contact the Chairman Concierge via email. I'll add more in the concierge section.

I think this one depends more on personal travel preferences. As you mentioned, premium cabin tickets are quite expensive point-wise with the TY program as opposed to with airline FF programs, so for a traveler that generally likes to spend points on those, Amex wins in my opinion.

Also, the Chairman card currently appears to award TY flight points if you pay the taxes on an award ticket with the card. This is assumedly not intentional and not a proper benefit, so your mileage may vary (quite literally), and expect this to disappear sometime. There are also reports of TY flight points posting without enough regular TY points to match, but if this is still the case, I'm sure they're working on fixing it.

In the US, Priority Pass seems to mostly provide access to DL, CO, and/or NW lounges in most locations, some UA lounges, and various others to fill in the gaps. So if you are a DL/CO/NW/UA flyer, there is a higher chance your lounges may be covered by Priority Pass than with other airlines. Of course, international lounge access is far superior.

The Chairman Card also provides coverage in various countries (Ireland, Australia, others) that Amex excludes. Not sure of the specifics on what Amex's exclusions are.

Also note that one can get Preferred Plus status with Starwood (Gold minus the 50% point bonus) by having a Starwood Amex at $30/yr. Of course this has nothing to do with either card, but in my opinion makes HH Gold slightly more valuable. And there are of course other ways to get status at each... so I'd agree this really is a tie.

I have used both for similar tasks, but not for the same task. In almost every case, the Chairman Personal Assistants performed the task better and more quickly. They have also performed highly involved tasks (involving calling quite a few foreign numbers to research various things) that I do not believe the Amex Platinum concierge would do. In my personal experience I rate the Chairman Personal Assistant significantly better than the Amex Platinum Concierge.

As I noted above, the Chairman Concierge can be contacted via email. Responding to a prior email from them works well, as should sending an email from a registered address. Additionally, they've been quite happy to call me back at an foreign number on a couple of occasions after calling or emailing them and requesting that.

I agree that someone needs to assign several varied tasks to both concierge services simultaneously to come up with a clear winner in an objective fashion.

Actually, if anyone wants to try this out, I have a good test case. I just recently made perhaps the oddest concierge request I've ever done: I was having an argument with a friend about the potential miniscule calorie content of Listerine Pocket Pack breath strips since they're obviously stated as zero. I emailed the Chairman Personal Assistants from a Treo and asked them to kindly research the actual calorie content of this product. About half an hour later they responded after having contacted the manufacturer by phone with the information I requested, along with additional details on the general makeup of the product and a list of ingredients. Anyone want to pose this same question to the Amex Concierge and see how well they perform?

Additionally, Amex seems to have the ability to occasionally find availability at restaurants that are otherwise fully booked, simply due to their brand name power with merchants.

* Customer service: CHAIRMAN

One button press after entering your card number and SSN with the Chairman Card. Amex's phone tree is a huge pain by comparison. Also, I have not once have had to hold for a customer service representative at Citi, whereas I have experienced long holds on occasion with Amex. The actual representatives seem to be more proactively helpful at Citi, as well as able to directly handle more tasks (e.g., card replacement, issues with other Citi cards, TY points, etc) than Amex, where you are often transferred with long hold times for things such as the above.