Thinking of changing from NPower and GB Energy Supply are the cheapest for us.

1) Are they difficult to deal with?

2) Is the whole switching supplier thing a PITA?

Not experienced them particularly, we switched from Npower to Extra Energy last year. They were much cheaper but it turns out their customer service is chronic. No bill received in the last 12mths so nearly £2k accrued in their DD system.

Umpteen emails later, now escalated to their MD. just to get a bill.

Good luck with yours !