INSTALLATION: both are easy to install, you only have to put a loader/create a folder on the SD card; then you just copy all your .xex and .atr from your PC without compatibility problems.
PROGRAMS SELECTION: both offer on screen selection, SIO2SD let you select programs from the lcd display too (useful to swap disks on the fly).
ON SCREEN MENU: SIO2SD displays long filenames of all files and file selection is quicker (loader v2.5), SDrive displays long filenames of selected file only.
NUMBER OF DRIVES/DISKS SUPPORTED: SIO2SD 15 - SDrive 4 (f.e. Alternate Reality, The Dark Crystal, F.R.E.E., Gunslinger need more than 4 disks)
SPEED: according to this thread, SIO2SD seems faster but IMO more tests need to be done.
SD CARDs: SIO2SD up to 32GB - SDrive up to 2GB
LAST SOFTWARE UPDATE: SIO2SD 2012 - SDrive 2009
PRICE: SIO2SD parts are more expensive but SIO2SD devices strangely seem cheaper. EDIT: recently AtariAge user santosp started selling cheap SDrives (look my topic for newbies).
VARIOUS CASES:
SIO2SD
SDrive
CONCLUSIONS: SIO2SD and SDrive are both good devices. SIO2SD has the advantage of drives/disks supported (15 instead of 4, important for some games contained in more than 4 disk), disks selection on the fly and loader long files names display (all files, not selected ones only); obviously with this device you can select .xex/.atr on the fly with the LCD display too.
Please feel free to fill voids, add fields and correct me if I am wrong.
I will update this post accordingly.















