I rarely throw any hard baits but here it goes. Crank baits are generally used to "stump bumping." You throw them and bump them off of the bottom and as they float up after hitting an object (and you stop your retrieve) that is when the fish will usually hit it.
Rattle baits are usually used in more open/deeper water were bass are suspended such as fish suspended at the thermocline during the summer or in open water chasing shad.
There is no, "one is better then the other" here.
If you are a beginner and doing summer fishing from the bank, I would suggest buzzbaits in the morning/evenings and some sort of soft plastic bait jerk/swim bait during the day like a Yamamoto senko, trick worm (bubblegum), or Yum money minnow.