In this circumstance, I'd personally go with Proxima Nova. If you do any online work you have the benefit of using the web version via @font-face.

Proxima Nova. Gotham is losing it’s cache quickly because it’s becoming a favorite of hacks who just slap together low-budget work with templates and popular fonts. I’m seeing a lot of it in drug store signage and store-brand products. Not something clients are going to want to be associated with.

Do I need a TypeKit account for the Proxima @font-face setup?

I just noticed that they've got different uppercase "M"s as well... I think I prefer Gotham's... but it's hard to make a choice like this based on one letter.

When will H&FJ fonts be web-friendly? Seems like they're the last to get on board.

Proxima Nova is great! That a was at first very unfamiliar to me, but I’m gettin’ there on that one. Another contemporary geometric (although not so strict) is Galaxie Polaris, and a typeface I find very interesting is the grotesque-geometric gap bridging in Graphik.

Shameless plug: You can get Proxima Nova + unlimited web license from Fontspring. Here's the link: http://www.fontspring.com/fonts/mark-simonson-studio/proxima-nova

definitely Proxima Nova, I think it has more personality than Gotham. Even in caps looks gorgeous: http://drbl.in/42345

I know I'm late to this party -- and the votes have been unanimous -- but the other positive thing I would say about Proxima Nova is that it has more sparkle and detail at display sizes. Gotham is so even that at larger sizes it looks a bit dull and monotonous. (I've seen companies adopt Gotham for their identity, and suddenly things are looking bland, bland, bland.)

I think Proxima is a font for a lifetime. Like all H+FJ retail products (with the possible exception of "Fetish No. 338"), Gotham was built to stick around, too. But I suspect designers will find objections to it based on how it's being (over)used, like those James "Dunwich Type" Puckett mentions above. Perhaps Gotham is Tobias Frere-Jones's second Interstate, a great face that's used too much and poorly.

James didn't make a plug for himself, so I'll do it. His family Armitage shares similar source material with Gotham (vernacular, non-typographic lettering from buildings), has a lot of nice detailing, and it's available for print and web licensing.