(Disclaimer: this is an unedited rough draft.)
I promised to not write about backpacks, but here we are. Let's just get all of this out of my system now so that I never have to write about backpacks again. I'm going to talk about backpacks that I use, backpacks that I recommend, and backpacks that I do not.
I'm mostly interested in bags that are useful for EDC and for one-bag urban travel. There's definitely a lot of other use cases out there (in particular bags for hiking and other outdoor activities), but I don't feel like I have enough experience in other areas to talk about them.
I've spent a lot of time thinking about bags because I used to travel a ton, both for work and fun. I don't quite buy all the one-bag gospel about how essential traveling with one expensive backpack is, but I do enjoy having a nice piece of gear that's easy to pack and use.
One trend that I particularly dislike is bags that are over 30L in size. At that size, you're essentially carrying a suitcase on your back. And, if you take advantage of all that space, your bag will almost be way too heavy to comfortably carry. Either pack less or bring an additional duffel/suitcase.
Conversely, one feature I find missing from a lot of bags is a dedicated water bottle pocket. Water bottles are often one of the heaviest and bulkiest items in a backpack, and not having a dedicated pocket for them means that they will either cause a weight imbalance in the bag and/or be hard to retrieve from the bag without needing to take everything out.
Bags that I currently use
This is my everything-but-EDC bag. I use this for pretty much all my travel, and it works as a one-bag solution for personal travel for any amount of time and for business travel for up to a week.
The Synapse has been superseded by the Tom Bihn Synik, and the Synik is better in many ways: dedicated laptop compartment, better straps, luggage pass-through.
However, I find the Synapse 25 a lot more versatile than the Synik 22 or 30: the size is just right, and the center water bottle pocket is substantially larger, which means it can be used for both a water bottle and electronics (Kindle, Switch, iPad Mini) for a flight.
This is my EDC bag. I use a 13" laptop for work, so it fits cleanly in the laptop compartment. Unlike the Synapse or the Synik, the zippers are only visible from the side, so it looks a lot sleeker.
In an ideal world, I would like to use the same bag for EDC as I do for travel, but since I already own this and the Synapse 25, I might as well use this bag so that my EDC is as small and light as possible. In particular, I find it might easier to keep this bag on my back when taking the subway or a bus, whereas with the Synapse I usually have to take it off to avoid smacking the people standing behind me.
Other bags that I recommend
If I had to start from scratch today, I would buy a Synik 22. It's somewhat overbuilt and kinda ugly, but it has the perfect pocket setup and can cover pretty much any travel situation.
Using something like the Synik for anything beyond a weekend trip takes a certain minimalist mindset when it comes to packing. But, fully packed, it's probably about as much weight as you'd want to carry on your back anyways for long periods of time.
The main flaw with this back is the laptop compartment's size. Despite the bag's size, the compartment cannot fit a 15" laptop, which means you need to carry them in the main compartment. The larger Synik (the Synik 30) can fit 15" laptops (and even the new 16" MBP), but it's so large that it's unusable for EDC.
Bags that I do not recommend
GORUCK GR1 26L
The GR1 looks good and feels good while you're wearing it. It's also really easy to pack, since it's just one big compartment. However, it's very heavy, the fabric is rough enough to tear clothing, Plus, there's only one external pocket, and it's hard to keep anything that's not book/tablet sized in there, because everything ends up at the bottom, and everything in the pocket bulges out. There's also no good place for a water bottle, since it's too easy to loose the water bottle in the main compartment, and the external pocket is useless.
Tom Bihn Aeronaut 45
The Aeronaut has a great pocket setup, and the 30 seems to be a really nice bag, but the 45 is not. It's very easy to pack, but it's ridiculously large and bulky when filled--you can't even carry it as a duffel easily because of how heavy/large it is. There's also no good place to put a laptop, which means the laptop ends up taking up a lot of the space because you have to pack around it.
Tom Bihn Synik 30
In theory, the Synik 30 should be a supercharged version of the Synapse 25. Though it's ostensibly the height/width as the Synapse 25, it feels and looks a lot larger. It's also noticeably heavier, probably since it has the added fabric for the luggage pass-through and laptop compartment. Finally, despite its increased size and weight (and price--the Synik is $90 more expensive), I found that I could not pack that much more in the Synik than I could in the Synapse.