I have 3 platforms actually
I have 3 platofrms atm but m dropping openvz to put the other two "on the cloud" platform setups as cloud hosting is Id say hands down the best seller atm.
OpenVZ u can use a free master software I think HyperVM is still free, used it years ago
but SolusVM is probably the nicest one for OpenVZ as it has modules in almost every billing software so u can automate vps creations.
I have cloud setup through another datacenter set on Xen Hypervisor that uses OnApp. While Im not particularly thrilled about OnAPP the ability to scale in 10 seconds when needed is awesome feature.
The most stable but also prob the most expensive possible is VMWare. VMWare is solid, havent had a single moment, one hickup form that node in whole time have had it. SO VMware the hypervisor you can get free, but if want the exterprise solutions for the easy tools and such it can get into many thousands of dollars quickly. If you can typea 2 sentence in command line u don;t relly need those toolsas much as some think. I dont even make templates, I build them from the OS isos and takes less then 10 min total. I just added SAN backup to the mix on vmware and adding a second node in datacenter the company is opening in few weeks soon as they open those doors.
With VMWare the failover isn't AS important as is on Xen or the others because it just doenst fail very often if ever like most of the opensource platforms tend to do more often.
The other thing need to consider is on OpenVZ u can oversell everything, on Xen setup u can't oversell ANYTHING and on VMWare u can oversell everything but the RAM being VMware reserves whatever RAM u give the vm as if its being used even when its not.
That is a big factor, especially if new to it, I know it has been for me. When people offer $8 vps plans you best belive they are overselling where its limited on other platforms.
Tons go with OpenVZ because its free, panel for it is cheap, easily automated and can oversell it to the max which makes it the most profitable I guess but I look at it as you get what you pay for.
Example I piad $90 for sneakers 14 years ago and JUSt threw them away finally, my kids get those cheap $20 ones all the time cause they are growing so fast and go through 3 pair a year so I did much better by paying more awhile ago Id say?