I guess everyone has a different opinion on what is best. I do not like splitting with the splitter in the vertical position, unless you have someone handing the logs to you reaching for new logs and getting the split ones away requires getting up and down or standing and bending over. either one is a back killer for me. I like a stand alone splitter because it allows me to use the tractor FEL to carry logs and act as a platform while splitting. I do not lift any logs till they are split this way. As far as having another engine to winterize that is nothing, either fill up with stabilized fuel or run the last tank dry. No big deal either way. I seldom need to that anyway because as soon as a good day arrives I am splitting wood anyways.
It would be nice if the OP could try out each method to see which is best for him.