once upon a time, ram(vishnu) and shiv had a fight. now ram is shivji's guri amd shiv is ram's guru, and they r one and same, so they made up moments later. however, on seeing them fight, ram ke bandor log and shivjike bhoot log also started fighting. they were so involved in it that they did not even. see their istas made it up. thousands of yrs have goje by, the bhoot and the bandars still fight on.
Staunch kali bhakts of bengal add another spice to this, and this is out of topic btw. Krishna is callee vaba par kandari.
So they say, our mother has lots of work to do, so she has kept a sailor as her servant to ride the boat and a cleaner(shiv) to dust the house. Bottom line, all r one and same but there is no arguing with blind monkeys.
There is oje more thing though. Shivpuja is the only puja which can be done by ajyone. Sanyasis who have personally left all their karma and having done their own shraddhas a can also do. Shivpuja. But u need adhistan to do Vishnu puja. Our house have all of them and ij this terrible summer, ky grandma puts all of them in the same swimming pool to cool them.