I never tried the Builders Breakfast flavour (or Onion Bhaji for that matter) but I heard good reports on both.
I tried them all (most from Home Bargains):
Duck in hoisin sauce: Nice, but nothing special.
Onion Bhaji: Absolutely disgusting, the worst of the lot! So bad I spat it out in disgust and got a drink of water to get rid of the vile taste.
Chilli And Chocolate: Almost as bad as the Onion Bhaji!
Fish and Chips: In a way, like Ready Salted crisps: you can take it or leave it. Nothing special.
Cajun Squrrel: Just normal cajun spice crisps with no hint of squirrel (maybe that's because they were vegetarian but still!).
Builders Breakfast: The best of a bad bunch. Not too bad actually. The one I predicted would win (which it did) - wonder if I could have put a bet on that?