For you, I would probably recommend the SSD for Trisquel (/ and swap), and
the 1TB HDD for extra data storage (/home). RAID is only really used in
enterprises, where continuous operation is required in the case of disk
failure; for simple laptop use-case by domestic users (or
non-mission-critical), you'd still have the other drive which you'd be able
to re-partition to install Trisquel onto, if one of the drives did fail.
RAID0 on 2 HDDs won't give much performance benefit in practise, and will
still fall below SSD speeds.
As long as you keep backups of your data (which is advisable anyway, even
with RAID) onto external data, non-RAID is fine for most people. With
SSD+HDD, you get the best of both worlds: fast operation for your OS, and
vast data storage besides that.
