Is it just preference to use fresh or frozen fruit? I sometimes think the frozen is sweeter maybe because it is processed more and I never really checked to see what was added but, if there is a difference other than preference what would the reasoning be?
Good ripe fresh fruit is better, just because its better quality. Another common option is juices (check they are free of sulphites and sorbate) or purees. Depends on the fruit though.
In most cases its recommended to freeze and thaw it anyway even if its fresh, because that helps release the sugars and flavours.
Wash any fruit you add with skin since you dont want the pesticides in your mead.
For some fruits that are added in high quantities pectinase is called for. Its an enzyme that breaks pectine, a very dense vegetal molecule. Without it your mead could end up really cloudy after the fruit (altough there is nothing wrong with pectine for your body. Its not bad for you).
If you do get fresh fruit, I recommend freezing it for 24-48hrs and letting it defrost before adding it, or pureeing it yourself. Freezing has 2 benefits: it can help kill any bacteria or fungi you don't want in your mead (should go without saying that you should wash it before freezing), and freezing will create micro tears in the fruit's skin so the flavor is better released. Pureeing yourself is just making macro tears to help release the flavor :P
Edit: damn it Dadux, you got in while I was typing mine haha