What type of sherry is typically used when cooking?
Cream sherry is very sweet - likely too sweet for most recipes that don't explicitly mention it.

If a recipe simply calls for "sherry", it usually means dry sherry, as that's the most common kind of available.  In fact, I don't think I've ever even seen "very dry" around here.  So I would definitely stick with the dry.

As for brand, if you see several different bottles all labeled sherry, I don't think it matters too much which one you pick - at least if you're using it for cooking and not drinking.

P.S. If you're using this as a substitute for rice wine, the commonly-accepted substitute is indeed dry sherry.