If you use a usb 3.2 gen 2 port, your max speed will be 1250 MB/s, pretty much every nvme ssd will be able to max that. Fast USB sticks will undoubtedly be very close, but might not have the same sustained write speeds compared to an SSD (With Dram cache).

If you’re just going to use it for recovery ISOs or installations it’s probably not going to matter much, I regularly use USB 2.0 usb sticks for that purpose just fine.

It’s up to you though, I had an nvme ssd laying around and bought an enclosure for it, I get about 1000 MB/s read and write with it.

So if you have an ssd laying around I think that would be a good option, but a usb stick will be fine as well and would be a little bit more compact, if that matters to you

Definitely go with an external nvme enclosure

Nvme would be much faster, I personally use the one from ugreen which is ~30€ plus a nvme with 2-3gb read/write speed for around 100€. You can find 1tb for 100€. I don’t know any good USB sticks that can do that much

USB flash drives usually use the worst flash memory available. There are good ones but they are hard to find and expensive. Going for a NVMe SSD in an USB-C enclosure gets you way more reliably better speeds and durability.

The flash drive will go full speed for a minute or a bit more and fall down to slow speeds while an NVME with a good enclosure that has a properly fitted heatsink can maintain much higher speeds indefinitely We’re talking 200 MB/s at most for a minute then about 50mb/s VS 800 MB/s the whole time

I have done some basic testing, and the speed of the USB stick you use does make a noticeable difference on the boot time of whatever you install on it.

If I recall correctly, A low speed USB 2.0 stick took around 30-60 seconds to load (either time to login screen or time to reach a blinking cursor for something like an arch install disk). If this is something for occasional use, even this works perfectly fine.

Slightly faster USB 3 sticks in the 100MB/s range can be had for only around $5-15 USD and work significantly better, maybe 7-15 seconds. These usually have assymetric read/write speeds, such as 100MB/s read and 20MB/s write, but for a boot disk the read speed is the primary factor.

Some high end flash drives can reach 500-1000MB/s and would load in only a few seconds. A high speed 256GB stick might cost $25-50, and a 1TB stick maybe $75-150.

An NVMe enclosure might cost $20-30 for a decent quality 1GB/s USB 3 enclosure, or $80-100 for a thunderbolt enclosure in the 3GB/s range so long as your hardware supports it, plus another $50-100 for a 1TB NVMe drive itself. This would of course be the fastest, but it is also bulkier than a simple flash drive, and I think you are at the point of diminishing returns in terms of performance to cost.

I would say up to you on what you are willing to spend, how often you realistically intend to use it, and how much you care about the extra couple seconds. For me, I don’t use boot disks all that often, so an ordinary 100MB/s USB 3 stick is fine for my needs even if I have faster options available.