I am currently with a host who has Ubuntu 10.04 LTS spiked (taking up CPU immediately after provision and never stops). The host refuses to acknowledge this as a high priority bcoz they dont have demand for this template. My question is, how much is HVM slower then PV? I may ask that particular host to move me to HVM instead
Very much depends the HVM configuration and supported hardware.
If you need something fully virtualized, HVM is the best option for you, especially when you have downtime and need to recover your data via the interface.
What we run HVM is slightly lower perfomance than pv itself. But, no benchmark done at this moment.
I don't think it will even be noticeable to yourself or clients. Meaning each one. Obviously your clients are going to want the one with the most features and easiest navigation. I would choose (obviously) the one that is raved about by fellow VPS users!