Well, it all comes down to batteries, brightness, and size. The PD30 will be the brightest but batteries aren't as easily avalible. The LD20 offers good brightness with common batteries, but it's gonna be larger. The LD10 is the smallest and only requires a single common battery, but you loose some brightness and runtime (I think).
If you have other AA lights already, the PD30 might be worth a look. If this will be your only light, I'd go for an AA option. If you're not worried about size or needing two batteries, and need the higher output go with the LD20. If you are thinking about carriability and/or survival use, the single AA LD10 may make more sense.
Personally, my main go to lights (Surefire 6PL and G2 w/led upgrade) both run off of two cr123 batteries, and I'm not happy with that. I am currently looking to switch to AA. I am willing to give up higher output for a more common battery. Specifically, in my case, I think the single AA light is the way to go. Not so much for the smaller size, but for the single battery requirement. I feel like a light such as the LD10 is bright enough most needs.
Another thought is to look at the 4sevens Quarks. With those lights you can buy extra battery tubes and switch (or Lego) the light from one or two cr123s to one or two AAs. I'm not sure if battery tubes are avalible for the Fenix's. If I recall correct, the Quarks wont have quite as high of output at max brightness, but the offer a lower low with a longer runtime.
Lastly, for higher output, you can use "14500" rechargable AA batteries and greatly increase output in both Fenix and 4sevens lights. I believe these are capable of taking the single AA up beyond the 2xcr123s output. Look into that before jumping into it though becuase it can be dangerous in some lights.
Also, I have owned about 5 Fenix lights in the past and have been very happy with them. I have yet to own a 4sevens light, but 99% of what I've read about them has been possitive.