The best thing you can do it compare apples to apples. Getting the best price at this part of the game is a no-no. A roof is one of the most important parts of the building, if it leaks, damage is sometimes not seen for years and the costs to fix are high.
Find a reputable company who has references of other jobs where you can talk to the other happy customers. Make sure they have liability and Workman's comp insurance and let them give you a copy. Ask for a 5 year warranty to sell the job, any roofer worth their salt will know this is not an issue.
Go with ice and water shield in any valleys and at the bottom 3 foot edge of the roof. Make sure everything laps over each other as you watch the job being done. Kind of like you don't tuck your raincoat into your pants theory.
#30 lb felt paper everywhere else. Try to spring for copper flashings , they will last the longest.
Gutters should be repaired and rehung if possible, only if their condition is OK.
Now is the time to run a bigger downspout also.
Make sure you have proper ventilation for the attic spaces, now is the time to ask them about continuous soffit vents and ridge vents. A really good roofer will show you pamphlets and maybe even a computer generated explanation of what these things are. Ask on the phone for examples of what they will be presenting, not only material samples, but how the roof system works.
Hope this helps you to find a really good one.