It really depends on upon your requirements. SolusVM is now opened by OnApp and is now from quite a while working for the new 2.0 release. The new release would probably be way better than most of the mentioned panels here.
From a business point of view, SolusVM and Virtuozzo are two good products to go with. If you need a free alternative then Proxmox is not that bad either.
We run Proxmox for a number of our customers have have been happy with it. The underlying virtualization is technology is all open source, KVM and LXC. Proxmox wraps a bunch of open source software into a nice, easy to use gui.
Their paid subscription provides support and easier upgrades.