Well I am a bit biased, as I am a realm only player. But in general there is no reason to not play on our server if your internet allows it.
Being part of the community / asking for help if you need it / trading are all awesome things. Also you get to use cool realm only items like the Creep. Finally from this season onwards, at the end of the ladder all characters will be preserved in non-ladder, so you won't lose anything and can keep playing them until Sigma comes if you wish.
About what is easier - it depends on your play style. Stormcaller is a bit harder to get going but makes some mid - end game content really trivial. Bowzon on the other hand has a really easy start but once you get to destruction and past the easiest ubers she is a lot like an Assassin - not really that straight forward.