Half Dollars:
1964 and before are 90% silver
1965 through 1970 are 40% silver
Quarters:
1964 and before, are 90% silver
Dimes:
1964 and before, are 90% silver
Nickels:
I keep everything 1959 and before
1942-1945 are war-time alloy nickels (35% silver) -- mid-1942 they started making them, so some are silver alloy, some are not. The ones with the mintmark over the monticello are.
Pennies:
1958 and before are wheat pennies
With any "silver" coin roll, you can look at the reeding. The silver coins will be have silver reeding. All the modern ones will have a copper stripe.
Snee broke down the years and silver content well. I would also suggest if you are new to coin roll searching,if searching halves, definitely look at all of the dates because some of the silver reading has fooled me a few times and I didn't think it was a silver half.
It is not better to in my opinion to search dimes and quarters because the odds just aren't that good. Some of the guys on here do very well with dimes, but I have never found any silver dimes or quarters while coin roll searching.
Whatever coin denomination you decide to search, I wish you luck.