Oyster and Visitor Oyster are more alike than they are different. They are both stored-value cards that deduct the price of trips as you make them, up to a daily cap. Journey prices and coverage are the same for both variants. Each kind of card can be topped up with cash or credit at machines found all over the system, if you find yourself using more than you loaded onto it from the beginning.
The differences are:
A Visitor Oyster costs £3 in addition to the balance you put on it, whereas an ordinary Oyster requires a £5 deposit. You can get the £5 -- and the outstanding balance on the card -- back if you take the time to queue up for a refund when leaving London; the £3 purchase price of a Visitor Oyster card is not refundable.
Visitor Oyster comes with colorful "look at me, I'm a tourist" branding on the outside, rather than the stylish blue of ordinary cards.
Visitor Oyster entitles you to some special offers. Unless you had planned to go to one of the participating places anyway, that may not be worth a lot for you.
Visitor Oyster is not for sale within London itself; it can be bought at Stansted and Gatwick Airportairports, though.
Regular Oyster cards can be topped up online, or registered in your name and set up to top up automatically from a UK bank account. This is mostly irrelevant for tourists.
Buying an Oyster card is simple -- just queue up at one of the Oyster-issuing machines, give it money (cash or credit, at least if you have a credit card that supports PIN transactions), and it spits out a card. No details need to be provided.