The all-out best, in my opinion, are Muir Glen Organic whole peeled tomatoes in juice (w/ a little salt added). I know that many people swear by imported Italian tomatoes (esp. San Marzano), but I've never found anything that's even HALF as good as the Muir Glen (which come from California, and are thankfully becoming more and more widely available). They make all the difference in the world in any recipe using canned tomatoes (and fresh tomatoes only taste better when their in absolute top season).
Curious what others think.