Every resort has their own chart, so there isn't "one size fits all." For example, at the ski resorts summer is off-season, but at the beach resorts it's high season.
Also - with fixed and float weeks - it just depends on your situation. If you buy a fixed week, and your work schedule or your child's school changes, then you may end up with a TS you can't use.
Once you settle on a resort or two, go to the forum on TUG for that site and see if the chart is at the top of the forum, or ask the owners there where to find it.