To be honest 2WD will make you better.
I try to do both. 4WD is easier for sure, They drive/jump 10 times easier than 2WD, I have never driven the old losi cars so i can't comment.
Id be looking at a 7.5t Combo, That was you can run either.
LRP are on of the best, But the ORCA combo is great value and top quality stuff!
Its down to you at the end of the day!
Drop by Sunday and have a look! (Shamless Plug!!) My 2WD RB5 is for-sale too