Never used HostBill & never will. Far too expensive & lacks tons of stuff...
The admin interface is extremely weird, hard to locate things & is complicated & the theme is completely nasty. However, I have known customers to use it without issue - my main issue is support for the software after the first year, which I find ridiculous ($50/ticket), if you have a software, you should support all your customers in my opinion, not charge them for support. Which is why I like WHMCS, they provide support & updates for a fixed annual price (I have an owned license, just fyi), which comes with unlimited tickets & updates within that time frame, which is acceptable, as I would expect to contribute to the further development of the software, but not on a per ticket basis.
We are in the process of migrating a client from Hostbill to WHMCS. They paid like 5k for the 'everything' package. And something like $50 annually for automatic updates, and the automatic updates have completed stopped working, reaching out to Hostbill support and they're extremely lackluster. For the amount of money this client paid the support should be bending over backwards to help resolve issues.
Speaking with the client I asked him what the decision process was like for Hostbill over WHMCS and it basically came down to a DCIM/IPAM module (which is available third party for whmcs) and the NOC-PS module. (also available third party for WHMCS)
Hostbill seems a bit clunky interface wise, it has a decent amount of features but the support is where they really seem to be lacking. For the pricing they should have much better response time and response quality.
Invoicing in HostBill and WHMCS is much the same. I find HostBill a little simpler to use, because you can select from your predefined products and set quantity per invoice line directly in the invoice, without having to make a quote first.
but hostbill does not at least have an online demo.