Ah, for me this is as hard to choose as my favorite song. >.<
The entire Inheritance Cycle, The Ranger's Apprentice series, and the Legend of Drizzt Series would be in the top three. I haven't a favorite book from any of the series so I'll just put them all together lol.
Legend of Drizzt probably has the best fight scenes and the most personality put into every character. Ranger's Apprentice is so realistic but so clever. The fight scenes are really cool in it, but it bases itself upon what happens behind the scenes of the fighting, the people who fight in the war before it starts (The Rangers) and it's a nice break from mythical stuff, but still has medieval basis, the only thing really fake about it is that it's in a different universe so to speak, but it doesn't base itself upon magic at all. The only time when there had been a possibility of people thinking that some magic had been involved, it was only clever illusions, someone using the environment to work with them. Meanwhile, the Inheritance Cycle has much better large scale fighting than the Legend of Drizzt, which is better with like one on one, sometimes two on two fighting, or like one person pwning a bunch of grunts or whatever lol. The Inheritance Cycle is much better than the Legend of Drizzt when it comes to actual wars. And the Inheritance Cycle... it just has something that I like about it lol.
Percy Jackson and the Olympians and Maximum Ride are REALLY close behind, but the three series I stated above are simply ingenious. These have a more basic level of thinking, partially due to them being first person.