In my view, the attributes which make a good canning peach, also make a good freezing peach.
You want the fruit to hold some texture in the freezer or in the canning jar. And you want a low browning peach. You also want a freestone peach.
Just about any peaches from the Redhaven season forward are freestone. There are a few freestone peaches before Redhaven, but the earlier the peach the more likely it will be a clingstone. Some years, early peaches will be more clingy than other years.
You can test a low browning peach by simply cutting it open and see how fast it browns. If it browns quickly, then it will have more of a tendency to brown in the jar, or brown when thawed after being frozen. You can add Fruit Fresh (primarily ascorbic acid) to slow browning, but it’s better if you start with a low browning peach.
Probably the most important thing to me is the texture. Any peach will soften when canned or frozen, but some are worse than others. Typically early and midseason peaches are very juicy and have a much more melting texture than late season peaches. This is good for fresh eating, but not so good for canning or freezing texture.
Late season peaches like Encore, Autumnstar, Victoria are much firmer when picked ripe and less juicy. That’s the nature of late season peaches. They make a much better canned or frozen product, imo.
A lot of people like to can Redhaven, but imo, it doesn’t make a very nice canned, or frozen product. It gets pretty mushy after canning or freezing. It does make an excellent fresh eating peach though.
Contender is perhaps a better canning peach, but still not as good as those really late varieties.
Some of the best canning peaches are what I call California canners. Those are varieties which hold texture very well in the can. It’s what you might find when you open a can of Del Monte peaches. The problem is they sort of have a rubbery texture when eaten fresh off the tree. I’ve grown a couple of these type of varieties and I don’t mind the rubbery texture for fresh eating, but the texture puts some people off. Also note that California canners are all clingstone peaches. Peach canneries have machines which can easily remove the pit from clingstone peaches. It’s harder to do it by hand. Vinegold was an excellent California canner. Very productive and very sweet peach. I got rid of it only because most of my customers want freestone peaches for canning, or peaches which have a melting texture for fresh eating.
If you are making smoothies out of frozen peaches, then of course the texture doesn’t matter.
The sweetness of the peach doesn’t matter much when canning or freezing, since it’s easy to add a little sugar and is what I recommend to my customers. A little sugar not only enhances the flavor, but also acts as a preservative.
There are a very few peaches which don’t blanch well. That is, the skins won’t slip very well after blanching. This makes a bit more work for the person doing the canning since they have to cut all the skins off, rather than blanching them off.