The following tarantula genuses are considered medically significant:

Stromatopelma
Poecilotheria
Heteroscodra

As for common names, the true featherleg baboon T is usually Stromatopelma calceatum. Ornamental tarantula's are Poecilotheria, or "pokies". Heteroscodra maculata is the "Ornamental babbon".

No one has ever died as a result of a tarnatula bite. However, being bitten by a tarantula of those genuses will probably earn you a hospital trip.

Old world tarnantulas (Asia, and Africa, for the most part) are more defensive, do not have urticating hairs, and have stronger venom. New World tarantulas (the Americas) have urticating hairs.

Most tarnatula bites involve a bit of local swelling, burning/pain at the site of envenomnation and possibly itching.

It is generally recommended that new people getting into tarantulas get a New World species first, and even then to get one of the docile species.

Scorpions vary greatly, as Shelby said. There are many more "hot" scorpions. A sting from a flat rock scorpion is considered to be weaker than a bee sting.
Hands off is usually the best route

I keep both Poecilotheria and Heteroscodra if you're wondering.