Sitka Spruce would be my number one choice. Its expensive.
Ive made many blades from Doug Fir which seemed to hold up fine for years in an eastern humid climate (right on the Atlantic, however Ive since moved to the northern midwest where its still a bit humid, but nothing like the east coast).
Im now running a set of Otherpower blades made from western red cedar. I keep a relatively thick coat of linseed oil on them, time will tell how they hold up, but I suspect they will be fine. I wouldnt use soft pine for structural reasons. Honestly, many types of wood will work as long as you can keep the moisture out.
The #1 cause of blade erosion (leading edge) is a high tip speed. If you plan to run MPPT controllers with these machines, prepare to perform a lot of upkeep with leading edge erosion, especially in a humid climate. Even professionally manufactured machines such as Bergey still have issues with LE erosion if the tip speed is not kept in check.
Most people that run the axial flux turbines keep them stalled to battery voltage, and that alone will make a wooden bladeset last a relatively long time, at the expense of a bit of top end efficiency (which is not really so important if its a battery based system usually -although there are system design exceptions). If its grid tie, thats a whole different school of thought, which you can design for if you are so inclined as long as you pay attention to the top end RPM and dont get too greedy. I personally like to run my machine in stall, its more peaceful and quiet that way, and the LE doesnt suffer such a pounding.
Leading edge tape tends to work well too. Ive had good luck with stainless steel tape. On larger machines, DanB has been using copper sheet, nailed and glued, to the outer 1/3rd of the LE.
I personally would stay away from aluminum blades. Aluminum tends to fatigue and crack very easily which wood does not. Wood tends to flex without fatiguing for a very long time and thats the main reason to use it, along with the fact that its readily available and easily workable.
RoyR