You're asking a very simple question with an extremely deep pit full of "if" scenarios.
First, keep in mind that no solid recommendation can be made without a good site survey. Without knowwing the environment (interfereance, potential for multipath, etc) any recommendation made is pure speculation, and as likely to fail as not.
Second, the AP is just a small part of the system. Given the information learned from the site survey, things like the type of antennas to use, power levels, and mobility features will probably be radically different from one scenario to another.
Other details, like the type of clients, security level, traffic (type of traffic, pattern of traffic, volume of traffic) is also necessary. Things like the mounting height of the antennas (ceiling, wall, cube partition ...) are also needed.
It's possible that you could get by with one 1200 series with a pair of "rubber duck" antennas .... it's just as possible that you'll need three or four with patch or panel antennas.
Because of local congestion or local AP count, you may need to go with 802.11a instead of 802.11g.
Finally, what's the budget (for hardware, software, management, and labor)? If the solution is more expensive than the cash allowed for it, what features are you willing to give up? How much performance are you willing to sacrifice?
These are things best determined by a qualified and experienced person on the site. Many of the questions can be answered with a good site survey, the rest are part of the interview.
There are probably many solutions that will work (to some degree), but for the money you'll spend, you almost certainly want to get the "best bang for the buck" in terms of throughput, reliability, and security.
Find a local reseller/partner and engage them to do a proper job.
Good Luck
Scott
