both of these billing systems are fighting in the small shared/resell hosting market. in reality both have advantages and disadvantages. You need to make that decision on what you will use after some reviews and research.
I do not think Blesta will replace WHMCS today, however things can change quickly. One thing about these solutions, is that Both have no ability to handle when a web host grows. Managing ports on switches, turning PDU power ports on/off, bandwidth management and billing, configurations to xen hypervisors, integration with various cloud software solutions, the list is long, actually very long .. but the market that needs these features is a lot smaller. I think Hostbill could have really changed the landscape, but at some point they decided they only wanted a niche market of higher end hosting companies that owned their switches, hardware, and needed really data center or fully cloud environments managed billing and automated solutions. Competition is good, period!
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