If you think of cloning your Windows installation to a bigger / better harddrive (or even a smaller SSD), you will first of all have to consider the difference between "classical" partition tables (which have been around for ages), and the new, fancy "GPT" partition tables with EFI partitions (which come with the "new BIOS" called UEFI; there are also "OEM partitions", which I hope to figure out as well).
I had read about all this superficially at some point, but mainly as a challenge to Linux, and without paying attention to possible Windows repercussions up-front. Like pretty much everyone else, I could only afford such luxuries as teenager... Anyway, you better google any details about all this if you're interested; this is more about early awareness and documenting related practicalities as I discover them.
There are many free tools allowing you to clone Windows even as it runs, but most won't work well with the shiny new GPT partition structures. And yet, even if you only need to clone classical partitions, you'd better stay away from Miray's HDClone. It does do the job well, but its free version is artificially slowed down to help sell the commercial editions. It used to be my tool of choice before I discovered how miserably it failed with GPT partitions.
Anyway, now I know better, and for cloning disks with classical partition tables I'd use AOMEI Backupper. It's really fast, easy to use, and Chinese - they're very open about the latter, so I suppose we're good on the paranoia front. Still, it won't do too well for GPT-type partitions (EFI, OEM, or even recovery), so on to more experiences.
In order o get these cloned adequately, I ended up paying the euro equivalent of roughly 20 USD for Paragon's Migrate to SSD, a horribly branded, but fairly proficient cloning tool. Downside: It clones only the system partition, the main recovery partition and the OS partition itself. Additional recovery, OEM and primary partitions I had were completely ignored. Note: It apparently allows you to do selective cloning in case of moving
a big, well-filled Windows partition over to small SSDs by leaving non-OS data behind, so if that's your usecase it may
just the tool you need. In my case trying to fill the "missing partition" gap with diskpart and AOMEI didn't succeed, so I grumbled, went and searched again.
And finally, at long last it seems that I succeeded: the free-for-private-use edition of Macrium Reflect at least copied everything just fine, with a confirmation of successful boot-up still pending at this point. It may have some forgivable UI deficiencies, and it is undeniably slower than AOMEI (120 instead of 90 minutes for 1 TB over USB 3.0), but at the end of the day it did the job. Two thumbs up! I'll report back in case it doesn't boot... :-)