Best Value is the same thing as
Position - I'm not certain on why they decided to call it two different things, but they are related.
Position is the numbering order you set where 0 is the "best value" and higher than that will come after.
So if you want products
A B C D to show up in a specific order, you would order them
2 4 1 3 to rearrange them as
B D A C - then select
best value in the sorting options.
You can also set the option to
name and they will sort alphabetically, or
price and they will sort by lowest to highest price.
You can set this globally in the
System > Configuration > Catalog > Catalog > Frontend area