Such a question is an open invitation to religious warfare. Everybody loves to participate, but nothing is ever settled.
If the question means “what kind of fencing is the most fun?” then the answer is: it depends what aspects of fencing you enjoy the most.
All fencing involves skilled timing, tactics and technique. Most épée fencers consider themselves practical, no-nonsense swordfighters who rely on as few artificial rules as possible. More visceral fencers who want to experience the adrenaline rush of a fast, aggressive swordfight will want to try some sabre. Enthusiasts of more medieval combat styles can try weapons such as the longsword at one of our half-day short courses or apply to us for individual lessons.
On the other hand, if the question means “which weapon is the most deadly?” the answer will depend on a lot of factors, not the least of which are the skill of the combatants, the presence of armour, the military and cultural context, and the rules of the fight (i.e. is this a street fight, a gentlemen’s duel, or open field warfare?). Most swords are highly optimized for performance in a specific environment, and will not perform well outside it. Comparing two swords from completely different historical contexts is therefore extremely difficult, if not downright silly.
Then again, perhaps the question means “which style of fencing is the most realistic?” It must be said that questions of realism have little relevance to an activity that has almost no practical application in the modern world other than sport and fitness. Historically, however, epees have the closest resemblance (among FIE weapons) to real duelling swords, and the rules closely relate to those of actual duels (sometimes being fought to only a single point). Other martial arts with a high realism factor include kenjutsu and some aspects of SCA fighting.