Hi Aaron,
For a scope of that size + the fact that it will be for your son (I assume visual only) then I think it would come down to price.
Personally I'd go for the 8" Dob as a first scope.
Here's another IIS thread on the SW135 that may interest you.
http://www.iceinspace.com.au/forum/s...ad.php?t=22930
Cheers, Bryan