The clean breakpoints I see are
5: Second Daily
7: Third Encounter
9: Third Daily
10: End of Heroic
11: Entry to paragon, "Name" level with the Name being your Paragon Path
16: Final feature of your Paragon Path, and sometimes the main draw of a path (like Malec-Keth Jannisary)
20: End of Paragon
21: Entry to Epic

Another option that might be decent for the E11 version would be feats after acquiring a certain number of bonus feats that allow you to get your U12, F16, and maybe even D20. That would probably be my preferred break point, since 11 gives you a lot of (usually) interesting build and tactical options, with the F11, E11, and your AP feature, while U12, F16, and D20 are a lot less commonly game changers, but can still be very interesting.