Commonwealth has won the hearts and minds of its large, medium and small business customers, but it has some work to do to please the microbusiness sector. In the latest DBM Business Financial Services Monitor, published yesterday, CBA was the top rated big-four bank in the first three segments but ranked behind Westpac with microbusiness customers.DBM found that on a whole-of-market rating all four big banks either held their ground or improved their ratings in 2012 - not a bad result when business conditions weakened and customers criticised their banks for not passing on the Reserve Bank's cash rate cuts in full.Big business customers (with turnover of A$60 million or more) are the most satisfied of all business groups. This is usually because they are treated to higher service levels.CBA's rating among its big business customers in December was 7.8 (out of 10). Its rating with medium businesses ($5 million to $50 million turnover) was 7.6 per cent, and with small businesses ($1 million up to $5 million) its rating was 7.5.Microbusinesses customers, with turnover of less than $1 million a year, gave CBA a rating of 7.3. The pattern was similar with the ratings of the other banks.ANZ and NAB were the laggards in all segments, although the margin in most cases was small.