I have an S4 although it has a large footprint, it is very light, and you don't always know you have it in your pocket.
I have to say it is probably the best phone I have had, from sony to blackberry to htc .....this one beats them.
Never had an Iphone, don't like them for numerous reasons.
I would pop in to a high street store and have a feel of all the phones available and see which one suits you best.