I have owned both over the years.(300ex and warrior)... I will list some differences and opinions that I have found.
-The 300ex is more compact than the warrior..giving you less room to move around on (though with your height..it may not make a huge difference).
-The 300 has a shorter wheel base...making wheelies a breeze.
-The warrior will also wheelie...It just takes a bit more.
-The reverse procedure on the warrior is better than the 300 ex.
-The warrior is a bit more powerful...and a bit better in mud.
-The 300ex tends to "two wheel" on sharp turns compared to the warrior. But that can be fixed with tires.
-The 300ex engine seemed to be a bit more reliable than the warrior (I threw a cam chain on the warrior..hard to tell what caused it..stretching?)
-Better gas milage on the 300ex...can go for ever.
-Better chain adjustment procedure on the 300ex. The warrior is easy to end up with a crooked chain or loose bolts.(as are all the yamahas)
-Airfilter on the warrior...bad design.

I'm sure there are more. If I had to choose between the two again...I would go with the warrior...That's only because it fits me better...I'm 5'11" tall.
-both machines are moderate jumpers...though the 300ex seems to more plush on the landings.

I liked both machines...and if I stopped to think more..I'm sure I could probably come up with more differences. BTW...I was not bashing either model..I like them both..I just out grew them for my style. But I will cause a little trouble probably.. Most people are usually interested in just one thing...Yes the warrior would win in a drag race stock for stock with equal riders. But not by a landslide.

good luck in your search.

The 400ex was mentioned...I have one of those right now. I don't consider it in the same league with the others. Does so much more differently..and it does it without reverse.

 

my post isnt as good as the previous one, but, I own a warrior, and i love it. then again, i am 5'10, and still growing. dirtwheels mag said the warrior is more comfortable for people 5'8 and over. but the warrior has more power

 

I own a warrior and love it. My friend has a 300ex that I rode for a while last night. I won't be trading in or selling my warrior for a 300ex. I didn't really like the lay out of it. The 300ex does wheelie alot better than the warrior and the warrior does have a horrible air box design. Both are good quads but when you are modding on, the warrior responds better than the 300ex. My friend is 5' 6" and he rides a 300ex. I'm 5'8" and ride the warrior. He rides the 300ex pretty good but complains about being cramped. My brother who is 5' even rides my warrior on occasion and he loves it. He said it's better than the 300ex which he's put lots of hours on. All in all though, it's all up to you. Ride both of them and make your desicion from there.

 

I would get the 300EX. I have one and I love it. I am also 14 but I am 5ft. 9in. and I feel very comfortable. I have never ridden a Warrior before but I think it all depends on rider preference. Obviously if you are smaller then you are going to like the 300EX more. Have you thought about getting a Kawasaki Mojave. It is even smaller and just as fast as the 300EX. I had one and it ran great for all the years before I got a 300EX. It just recently bit the dust. This is probably because I gave it to my little 10 year old brother when I got my new 300EX.