If you're burning firewood full time for heating then it's best to just purchase a log splitter instead of renting a log splitter.
Renting a log splitter once or twice is cheaper than buying a log splitter but if you're needing to rent the log splitter every year for splitting wood then the cost would be higher than just purchasing a log splitter.
Also with renting a log splitter you have to work to get the logs split during the rental time before you have to take it back or be charged more.
Owning log splitter you can keep it forever and split the firewood when you feel like doing it and don't have to worry about taking it back or damaging it even.