Well, surprisingly I found it extremely difficult to choose a favourite, in fact I chose both the African and American specials on the basis that I've rewatched those the most. They just have the best flow somehow.
I might define "best" as having the least annoying bits in it. So putting the specials in order of that:
Botswana special - nothing annoying about it at all. Basically perfect.
American Southwest Special - roadkill camping and Alabama. Skip those and it's pretty much perfect.
Vietnam Special - have to skip everything until they set off, and then JC obviously deliberately choosing a scooter and then bitching about it.
Bolivian Special - taking so long getting the cars off the raft when you could've just driven them off, Hammond's screaming in horror and other lunacy making it into the final cut, JC leaving them on the death road, May choosing an illogical option (I can't believe there weren't any old Jeeps for sale), and all round very generic music.
North Pole Special - have to skip everything until they set off, and after that I find the premise of racing some dogs a bit stupid. Wish they'd raced snowmobiles.
Winter Olympics Special - haven't rewatched this once I think. Or maybe just once. Reading about it here sounds like there was some genuine shit in there.
Interestingly, if I were to rate all these eps, I think the Bolivian special would receive the highest rating, because I always rate TG on other criteria: how it makes me feel, and for obvious reasons usually only in the context of the running season. The latest special was a genuine rollercoaster of emotion from annoyed, to happy, sad, amazed, scared, excited, relieved, envious, not in any particular order. And since S14 has been mostly shit the episode really stands out as a 10/10.