Well...not sure the exact question you are asking since all three of those can be one and the same. Not to mention PC's have a very wide variety of hardware choices. Then you say tablets results are so low. What do you mean so low? As in you aren't turning in as many per day? Are you getting low point rewards for each work unit? What do you mean?

The problem with going tablets is the up front cost vs. long term investment. If you are buying these to make a farm out of, it probably wont ever pay for itself before the hardware is replaced or just dies a natural death. These devices should only be bought for normal use and then DC'ing as a side benefit.

VM's are great. They allow you to use systems that you are less familiar with on machines that could have multiple uses. Keep in mind that AMD is releasing Opterons that have ARM, so Android on those devices will be an option. The downside is that Android does NOT have a full x64 version released right now. That is where the big gains under Linux tends to be. WCG also does not have an x86 Android app available, so it limits your choices even further. However, Linux x64 seem to do a lot better with the VINA apps. If you are a Windows person like most of us, a VM with Ubuntu x64 could wind up being more efficient than running under the core Windows OS.