I have used and liked both of those and also the REI Flash 18. The Sea to Summit is only 2.4 ounces and works great if you don't need to carry a lot of heavy stuff. The Flash 18 weighs 12 ounces and works better if you need to carry more weight. The Flash 22 weighs 17 ounces and carries a good bit more in part because of the pockets. The 22 also gives more easy access to your stuff with the extra compartment and pockets.

If you want/need to carry even more the Flash 30 or the Flash 45 might be worth considering. They are more pack than I personally use for day hiking though, but I am a bit of a minimalist.

I use the Flash 45 (2lb 2oz) for week long or longer hikes and even have used it on trips requiring a bear canister. For folks who lug more stuff it might be a day pack. It won't stuff into a pannier very well though.

The Flash 30 would be OK for the minimalist on hikes of a few days or maybe longer if restock opportunities were frequent and no bear canister was required. Most folks probably use it as a day pack. I am not sure they still make this one. Like the 45, it also does not stuff in a pannier as well