For everyday use, I buy Princes Yellowfin Tuna in brine (it comes in a yellow tin) - I get this from Morrisons. I prefer it to the John West that I have tried.
If you really want nice tuna, I buy Sainsburys Taste the Difference Albacore tuna - it comes in a glass jar, but it's pricey! So I only use that for nicer dishes I make with tuna - like extra fancy tuna sandwiches or tuna pasta, etc.