Ok, so what do you have now, and what are their symptoms?
Without knowing what's going on with your system atm, anything suggested could only exacerbate the issues you're suffering with, not to mention make it harder to pin down their causes.
On the basics, platters will last longer before developing errors, but are slower and difficult to find in "low" capacities, especially new. Solid state such as SDHC and CF are readily available but tend to give up much more quickly than traditional platters unless you're paying out serious bank. USB.... Just don't go there unless you have to as far as booting goes, it'll slow your system down due to all the interrupts created during transfers and really offers you nothing over what you'd get with either CF or SDHC.
I've tried a multitude, so just combine these options...
A4000T scsi
A4000T ide
A4000D ide
Quickpak 060 desktop version with scsi
Warp Engine 3040 scsi
Deneb USB (DMA and PIO, ZIII and ZII)
Misc. ide drives, 120GB-200GB
Misc. scsi drives, 9GB-72GB
4GB USB thumb drives
USB-sata enclosures with 80-250GB 2.5" and 3.5" drives
Normally a ~1.7GB or less System, no more than 1.7GB Work.
The constant has been OS3.9. As I said, I thought this was the gold standard, newest to use with fixes for drive capacity.
This was in 5 Amigas (3 4kD, 2 4kT) with 3 CPU and SCSI cards.
Closest yet was the Warp Engine SCSI. It copied far more files without issue, from one old scsi drive to another new SCSI, but it's seems to have developed RAM and heat issues.
The Warp Engine HD also included an OS3.9 that was NOT installed by me. I have no idea what was done to it.
I fear screwing up that drive by installing my 060 and other libraries on it so I duplicated it and tried with two other controllers and CPU cards with no better results.
Of them all, the Deneb/thumbdrive combo felt fastest in use, but was no more reliable.
I'll take stable over fast BTW.