Who's best to grade my coin?

The top 2 grading companies are PCGS and NGC, you need to go through a dealer to have them submitted. As for modern gold bullion coins most grade MS-69 or PR-69 anyway why bother with the added expense unless it would be safer if you had it slabbed. Some people are not to careful with coins or like to show them off, better to scratch a slab than a coin. There are 2 other grading services that have a good reputation on you have to join ICG the other you can submit on your own ANACS. The first 2 I gave you seem to be more dealer friendly so may add a little more value to your coin.

Go with either Professional Coin Grading Service (PCGS) or Numismatic Guaranty Corp (NGC). Your coin will be graded and certified as genuine (unless it's not).

It will be well worth it for the 1909 S VDB cent, but probably not for the modern bullion gold coin.

Here's more on certified coins:

http://www.valuable-coin-stories.com/us-certified-...

and here's more on your 1909 S VDB that you may find interesting:

http://www.valuable-coin-stories.com/1909-vdb-penn...

if you want it professionally graded you need to send it to a Third Party Grading (TPG) service like PCGS or NGC.