To summarize.

It depends on how many times you will ride the subways or bus to see which will be best.

Four rides a day - Pay $7 for a metrocard, you get a card worth $8.05, which is good for four rides. You get a fifteen percent bonus on cards of $7 or more. Up to four people can use one card, it will calculate the fares necessary each time it's used

Over four rides a day- the one day metrocard at $7.50. Note that a new day starts at 3 am every night from the first time it's used, not a 24 hour period, so it won't make any sense to get one to make a one way ride to the hotel and crash for the night, as it will reset at 3 am. Every person will need a card.

If your plans have you taking over four trips a day for four days, the one week card (to add to the confusion that expires seven days after first use at midnight, not 3 am) is the best deal.