Which sized speaker is best depends on the size of the room, the overall design of the speaker and the amplifier which is driving it. There are obviously good and bad examples of both big and small speakers.
As I become a more experienced listener, I find myself generally preferring large stand-mounted speakers controlled by a high quality, high current/powered amplifier in the vast majority of UK/European sized rooms. I find them to be more accurate and less likely to have overblown, boomy and indistinct bass. With floor-standers, the cabinet (because there is more of it) has greater influence on the overall sound quality/performance of the speaker. There are always exceptions to the rule but generally speaking, large floor-standing style speakers are less accurate and more coloured than stand-mount style speakers. This is why you rarely see floor-standers in recording studios. Up until a few years ago, I generally preferred floor-standers to stand-mounters for their greater scale and perceived low end. Now, I find the opposite to be the case in most instances.