Your billing system is more of a preference really, I prefer modernbill because of how many options it has. You can use it with cPanel/WHM, Plesk, Direct Admin, helm, etc. while with WHMAP I believe is only for cPanel/WHM.
There are both positive and negative's if you choose either one. Like I said earlier, ModernBill has many more options. You can fully automate billing, but it is a pain to set up, and the support isn't really something to brag about either. WHMAP is a lot easier to set up, so if your on a strict schedule or don't feel like using up a lot of time to set up ModernBill, go with this. The support is a lot better as well, they have pretty quick responses.
I believe both have a 30 day trial period, or some type of trial period. Try both of them out to see what you prefer.
As mentioned by my colleague ModernBill is superior to WHMAutopilot in many ways. I personally used WHMAutopilot since it's early days simply because it was so easy to use. However ModernBill seems to have things a bit more stable and it's advanced features are better if your offering full services hosting.
I would have to agree. ModernBill is the winner all the way. WHM AutoPilot isn't as advanced as ModernBill is... I haven't used the new v3 version that has been released yet.. But, when I previously used it then I can honestly say that ModernBill is a clear winner.
ModernBill can be modified much better than WHM AP to suit your needs.
It's also the most advanced
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