You don't need the most powerful one, but you do want one that can at least adjust the power down to a quarter watt (21 dB).
The maximum FCC allowable effective radiated power (ERP) for multipoint-to- point (an omni directional antenna to a directional client antenna) is four watts (36dB).
You want to get your system gain from the antenna, so you could use a 15 dB gain omni access point antenna. That will give you 15 dB transmitter gain AND 15 dB receiver gain. So....
36 dB (max allowed) minus 15 dB (ant gain) equals 21 dB (transmitter power)
Running a one watt transmitter (30 dB) means you can only use a 4dB gain omni antenna...which will give you only 4 dB receiver side gain.
Of the three you are looking at...
The PePwave can turn down to 200 mW (23 dB) and has a 5 dB gain antenna. Which brings us to the next question. Do they have other type certified antennas with higher gain? Buying a third party antenna that isn't certified for use with a particular transmitter is not allowed by the FCC.
The Alvarion devices are very expensive, and very reliable
The D-Link you mentioned isn't outdoor rated and may not deal well with hot weather outside.