Advice on mortgage x

2 mortgages advice! Please help x
The house I live in currently has 20k left to pay off - I am overpaying by the maximum £500 month (hard but long term gain!) and will have paid it off in 2.5 years . My mortgage fixed rate (6%) due to expire in June.I have another house that I rent out and have 80k to pay on that - but the rent fully covers the mortgage (only just!) that mortgage was fixed at a similar rate but recently expired so I have automatically gone on to their usual rate - which is cheaper (£50 month)
My question is should i borrow against my other house to pay this one off? The rate is cheaper on the other mortgage (but I can change this one soon) and I will have an early repayment fee (this is an outrageous concept I think!) but is it better that I put an extra £20 k on the other mortgage and be mortgage free here (and £800 a month richer!) or should I carry on with the original plan? Having the £800 month extra means I could over pay a bit on the other mortgage?
Is it better to have one mortgage than 2?
Thank u lovely people xxx