Trust me on this one: stick with the semi-western. It's a far more versatile grip. I was taught a semi-western grip, but I love spin, so I changed to a full western when I started high school tennis. Just about 2-3 years ago my coach switched me back to a semi-western and it makes everything easier. I rely heavily on my serve to help setup points, so if I'm not at the net volleying, I'm usually approaching and hitting a low ball. A low ball is the western gripper's worst nightmare because to get enough forward movement, you really need to whip the snot outta the ball to make it an effective approach. With the semi-western, you can more easily flatten out the stroke to give it more depth and give your opponent less time to get to it.
Do note that there are uses for all grips in the game, but for example, if I'm pulled out wide and know that if I put the ball back in play that the entire court is open, I used to take advantage of my western grip and flick it cross court and short into the opposing service box with a large amount of top spin, making my opponent either go for a low percentage down the line, around the doubles alley winner, or hit it right back to me once I've recovered. You can do the same thing by using a reverse forehand with a semi-western and get the same results. So my advice, having gone from semi, to full and back to semi is to stick with the semi.