wow, lots to choose from... I think we'll all have our own favourites here and for various reasons so if you're thinking of getting some- it will depend on what you like...
I personally like the Thailand Black (Haplopelma minax) tarantula and the Heterometrus spinifer scorpion. The thai black is very aggressive so always fun to watch and the scorpion is slightly more aggressive than the imperial scorpion so...
Depends what you're looking for though - think I mentioned this in another post. Burrowing species tend to be more aggressive but they like to hide so you might not get to see them much. Terrestrial species are more docile, can be quite pretty like b.smithi but just kinda sit there *display species*. The arboreal species can be very beautiful, moderately aggressive but require a bigger setup...
This is from experience so far so anyone feel free to disagree if you feel differently