X-10 had me at price; Control4 is 5 times more expensive on components, and Control4 gets real testy if you want to install yourself.
X-10 owns the patents and their technology has been around since the '70's Radio Shack days (elderly mom still has an X-10 system from that era, works like a champ). Control4 uses borrowed technology.
The bottom line is, If all you want to do is dim a few lights and control the TV, X-10 will get you going for less than $90. If you want the contractor/Control4 company to install a whole house system and for them to control your home control life, pick Control4. And have deep, deep pockets.
Here's an article:
X10 ‘Practically the Same Thing’ as Control4, Only Cheaper - Article from CE Pro