IMHO...more bands provide more control, but are more complicated and confusing. Many bass players prefer a 3-band EQ and rarely touch it. I generally like my amp have to have 4-5 bands of EQ and make adjustments on almost every gig to offset differences in acoustics.
For an amp's EQ to work for me, the bandwidth and frequency centers of the tone controls have to meet my specific needs. Another player may not be able to dial in the their sound with the same EQ section because they want to peak or cut at different frequency centers. One way to make amps a bit more flexible is to make a couple of the EQ bands semi-or fully-parametric. For example the Ampeg SVT's mid control with selectable frequencies is essentially a semi-parametric EQ.
If I am using outboard gear for tone sculpting, I want either parametric or 31-band graphic...but that is my preference. Why? If I need more EQ than my amp has, the EQ needs to be as precise and flexible as possible. I have a 10-band MXR KFK EQ on my pedal board, and sometimes I cannot achieve the desire results because the frequency centers are in the wrong place to compensate for a specif room anomaly or to produce a specific tone. Never had that problem with a good 31-band graphic or 5-band parametric.