Where are some good spots to chop mahogany trees.

i dont think there's any other place other than in the tai bwo wannai thingy. the mahogany trees in miscellenia do not give logs.

Your going to have to go out of your way to get these logs...but there are a few place to get them. These places are Tai Bwo Wannai tree grove, Kharazi Jungle, on Ape Atoll, Mos Le'Harmless (must have completed Cabin Fever quest)

which of those are the best it terms of speed

As long as you have the tradins sticks needed to use the postal service Tai Bwo wannai is the best place.

 

 

 

Mos'le harmless : The spot I know of is 2-3 minute away from a bank and has 2 distanced trees, unless there's another : no good

 

 

 

Kharazi : Never tried but if you can find a quick way to get trough the jungle, and if you use the karamja gloves 3 it could be quick

 

 

 

Ape atoll : With ape atoll tele this could be good, you have to try it out