I like U-Switch for comparisons, though my latest switch was done via the MSE Energy Club.
As already said, be very wary of some of the small companies. Like your last supplier, a number of these have failed in the last year, and more are expected to go the same way in the near future.
I personally, in common with thousands of other customers, it would seem, had a lot of problems with one called Outfox the Market, which seems to be marketing under various names now, including Foxglove Energy. I recently 'escaped' from them, and based on my own experience, my advice would be to avoid them like the plague
Check out review sites, but be very wary of any companies who appear to be having a lot of customer reviews removed from these, or where nearly all great reviews are based purely on the sign-up process rather than longer-term customer service issues.
Be aware that the best deal for you depends where exactly you live, so you definitely need to do your own comparisons based on your address and postcode. What's on offer on one area will not necessarily be available in another.
I have just started the search for my mum's next supplier today, so I know what a palaver this process is and sympathise with you.