Unless you want to sale premium support you would surely settle for the free inbuild WHMCS version. Definitely lucks a few things but works perfectly well for most support tasks.

Kayako is best solution!

Figured I would also add SupportPal (formerly ArcticDesk) to this thread. SP is built by the folks behind LicensePal and seems to be a great cheap product.

It appears to be more of a Kayako 3 type product in terms of feature set so not as advanced but at the same time not significantly cheaper than Kayako 4.

kayako one of the best ticketing system

We really like HostBill, as it integrates all of your automation, with a very good ticket system and live chat. Live chat and ticket system has macros (pre-written answers for common questions) and the ability to link a knowledge base (also included) article.

Kayako is the best option and a classic one. there is no comparing it with the whmcs help desk

While the 'best' anything is going to be subjective (personal preference), selecting a helpdesk that's continually buggy and continues to stall development is not really the wisest choice for the 'best option'.

I do agree that WHMCS needs some helpdesk work, however it's getting there, especially with improvements made in 6.3

WHMCS is a good ticket support system and there are also many 3rd party add-ons to integrate with your hosting website. This makes it easy to use

We are using WHMCS. It handles signups, billing and support pretty nicely.
It is one of the most recommended ones for this kind of businesses.

I prefer to use WHMCS system, the user only need to log in to one system for billing and support. Customers don't like to have to log in on 2 different systems.

WHMCS - The World's Leading Web Hosting Automation Platform is the best.

For me, built in WHMCS ticket system is a good choice.

We use ZenDesk and use Module Gardens WHMCS plugin to integrate and sync tickets - for us we like

Dave

Kayako just can't go wrong with it.
WHMCS has built in support for it.

We use the built-in support module in WHMCS.

If we need an external helpdesk we will use Hesk or OSTicket, as these are both very nice and FREE solutions.