ExtN usb disks mount options
 

When using usb disks, there seems to be a difference in how they are mounted, based on the filesystem type on the disk.

Vfat disks are mounted read/write for users, while extN filesystems are not.

While I can fix that for individual devices, I would like to find a general solution, so that any usb storage device with any filesystem is mounted read/write for users.

I'm using arch linux.

Do you know how to do that?

There's a very good reason for this difference.
For vfat & ntfs, because they do not natively understand Linux permissions, a generic set of permissions is grafted on during the mount process. For most distros, this gives everyone full read/write access to the partition.

While on ext2/3/4, they do understand Linux permissions & so you have the chance to set or change these permissions for every partition (or device in your case). After you have mounted a partition to a mount point, you need only to change the permissions on that mount point & it will remember it. For example, if your device is mounted at /media/disk and your username is alund. This is what you could do to give your user access.
This sets your user alund as the owner, so now you have full access. If you want everyone on your system to access it, you could also do this:
The filesystem on the device will remember these changes.