Hi Alex,

Both species would work...but again, it's about many other factors. This link can offer many of the consideration that need to be evaluated and understood...as well as other factors:

http://www.timbertoolbox.com/Calcs/beamindex.html

This really isn't a realm of "plug in" information regarding size/species/grade...without knowing many other pieces of vital information ranging from your skill sets to what type of joinery/housing these timbers will have, is this a traditional "green wood" (aka rough lumber) project...etc...etc.