For a historical perspective (hey, I am a history buff) the ancient Romans
used beech for their planes.  Roman planes, I am sure were made of beech-
at least the ones that have been found in various places.  Yes, 2000 plus
year old planes, some of which still had some wood remants!

  I know that some ancient Roman relic planes have been recovered from
Egypt which had  beech still present that was identified positively.    I
know that they found some in Germany not too long ago (maybe around 2001 or
so), and of course there was a famous hoard that was found near Reading in
England of (I can't remember exactly) maybe 60 or 70 tools in the 18?  Plus
there have been several old Roman ship wrecks with perfectly preserved wood
(wood does not rot under constant conditions of moisture, esp if the oxygen
levels are low- witness old Greek and Roman era wharves and sea walls and
bridge foundations that still have intact pilings, although all the above
water stuff is long gone)
  During my various visits to Europe for business, I have done some museum
and tourist things, viewing several different sculptures, funerary markers,
paintings, frescos, and even mosaics showing various Roman tools, including
wood planes. It is remarkable how similar they are to modern planes, except
that they used a transverse iron rivet across the escapement rather then
the typical sidewall groove for wedging the single blade (I don't think any
planes used a double iron until the early 1800's).  They tended to have a
York pitch (ie more than the typical 45 degrees, if I recall correctly).  I
recall seeing a relic that really reminded me of a mitre plane, with iron
walls and wood infil.

 So we have at least a 2500 year history of beech use for planes, and if
there was something better, I think you can safely bet we would probably
know about it by now!
Cheers from sweltering Waterloo
Claudio