I'm actually going to agree when it comes to Missouri, because it's an example of a seal-bearing flag done properly. Most just seem lazy- "Quick, slap a logo on a blue sheet!"- but there's actually a bit of consideration as to the composition of the seal in relationship to the tricolour on that one, and it remains distinctive even if the detail of the seal can't be made out, so it gets a thumbs up from me.
I agree here--I don't mind seals if they are well-integrated. For sub-national units, a seal defacing the national colors works as well (except in the US, unless you replace the stars with the seal and leave the stripes). Missouri did it well. Even Massachusetts because the colors are simple and the text is small. Gold figure on blue shield on white.
The lone symbol on a field is always a great way to go. Alaska, New Mexico, thumbs up. Indiana should also be in this category, surprised it didn't get more votes. Sure, it has tiny text, but it's barely noticeable!
I hate the Hawaiian flag. At most, two colors in your stripes, not three in a non-symmetric pattern! Colorado's stupid pacman design also gets a thumbs-down. I like Ohio because of its atypical shape and use of the national colors. Also was born there so I suppose I've gotten used to the pennant shape. The new Georgian flag, if it didn't have words, would have been a shoo-in for the top as well.
As for territories, Puerto Rico has a nice, heraldric flag and the
American Samoa has an interesting-looking one. It's striking, even if a bit complicated on the eagle.
Here's a link to the
city flags, which are more hit-or-miss. I like the
City of Washington flag as well. Simple, two colors, kid could draw it from memory, and it's George Washington's coat of arms (historical significance: check). Other ones like Indianapolis, Wichita, St. Louis, and New York look good. Boston is boring, and you'd think a city with that kind of history would have one that pops. For a spectacular flag failure, look at
Easton.