thinking on convert a 2.5 or 3.3 revo

[timaneli]

after i finished my kyosho mfr brushless project is now time for a revo 3.3 project finally.
i got a used by 70 dollars here in portugal and now i need tips!!
what´s the best gearbox to fit there instead original nitro transmission.
i can´t decide between e-maxx ones of the 3906 old model one and the one of 3905.
which one give best fit one the 3.3 chassis?

thank´s in advance