Avis is one of my preferred car hire company and if you book through the British Airways Executive Club you can earn Avios and you get a free additional driver too and generally better pricing if you book through the BA site, although I would always compare both for full transparency.
I've hired card in the UK and abroad and had good experiences with Avis, particularly those situated at the airport. The car we had in Canada was brand new (less than 100km on it) and spotless. We have never had any issues with the rental vehicles we have hired and we have always found staff helpful and not pushing selling 'extras' such as additional insurances etc.
If you are looking for a well known, reliable brand I'd definitely book with Avis if prices are competitive.