WELL.
Anything's going to be an improvement on Sainsbury's continental blend. I don't mean that to be harsh... It just will be. Unless something goes horribly wrong
I haven't bought much pre-roast recently so don't feel incredibly well positioned to offer an opinion. If you're after a single origin (well worth exploring at some point), several are being touted / loved on the main page of this forum
. There are also some solid staple blends...
Square Mile's winter espresso blend is absolutely blinding... Really complex, berry-fruity, and deep:
http://shop.squaremilecoffee.com/produc ... r-espresso
Steve's Perfetio blend has a thunderingly good reputation, and was absolutely corking (and beautifully tolerant / forgiving) last time I tried it:
https://www.hasbean.co.uk/products/Braz ... -Crop.html
Tolerant may be A Very Good Thing if you're new with the Gaggia. Steve's Perfetio is an incredibly solid workhorse in that respect. Temperature tolerant, very friendly, very well balanced. The Winter blend is more of an explosively interesting blend (IMO), but you might struggle to get the best out of it (and might have a steeper learning curve).
AND James' Formula 6 is a traditional favourite. Though - as mentioned above - given the choice, I'm personally choosing to stick with HB / Square Mile at the mo. Or - at least - until I hear more outrageous praise for James.