Credit unions received strong marks for their member service at branches, the ACSI noted. In addition to having very courteous and helpful staff, members said transactions were quicker and more efficient compared to banks.

Almost three-quarters of all credit unions offer free checking compared with about one-third of banks and they typically offer lower interest rates on loans and revolving credit, according to the ACSI. These were major reasons that customer satisfaction with credit unions climbed 3.7% to an ACSI benchmark of 85, a good deal higher than for banks, large (73) and small (83).

Members also touted the wide variety of financial services offered and that accounts were easy to manage and understand, according to the ACSI. Credit unions also do a good job at providing multi-channel services, with members giving high marks to both websites and call centers.

The ACSI also found that unlike bank customers, members are of the opinion that their current credit union offers competitive interest rates.

Still, despite all of their benefits, members said the lack of convenient ATMs and branches were the most troublesome aspect of their service experience at credit unions, according to the ACSI. The report noted that banding together with joint ATM network access is one way that credit unions have been able to fill this void.

Credit union membership has swelled in recent years, hitting a record high in 2011, breaking it again a year later and on target for another record in 2013, the ACSI pointed out.

Meanwhile, overall customer satisfaction with retail banking is back to its pre-recession level, the ACSI said. Despite rising bank fees, customer satisfaction for banks grew by 1.3% over the past year to an ACSI benchmark of 78, which was up one point from 2012's mark.

JPMorgan Chase maintained the lead with a 3% gain to 76, while Citigroup jumped 6% to 74, and Wells Fargo edged up 1% to 72, the index noted.

While Bank of America registered its largest improvement in a decade (+5% to 69), it remained in last place, and is the only bank that has yet to restore its pre-recession level of customer satisfaction, according to the ACSI.

“Even though banks have raised fees again, the 15th straight year of such increases, no negative repercussions have been detected regarding customer satisfaction,” said Claes Fornell, ACSI founder and chairman.

He added, “In part, this is because a fair number of consumers are changing their behavior to avoid the fees by exclusively using their own bank's ATMs and maintaining sufficiently large account balances.”