I did a gate a few years ago and posted about it on here:
http://www.tractorbynet.com/forums/projects/290381-driveway-gate-how-questions-challenge-2.html
After a lot of research I ended up with a swing gate 8' high and 14' wide with stone pillars and lights on either side. I went super high end and used FAAC openers and a Linear RE-1 Entry system. The goal was to have something that would last 20 - 30 years with no maintenance, look good and be openable via phone, key code or clicker. In my case I wasn't concerned with security so I did not go with a a lock mechanism, though they're relatively cheap. Some things I learned / considered that might be helpful for you:
- The swing gate is safer than the sliding gate (mine has no pinch points except where the gates meet and the pressure is so minimal it wouldn't injur anyone). A neighbor has a sliding gate and it seems like they had a lot of issues
- The swing gate requires 2 operators (more $$) and power / control lines to each side, so you need to go under the driveway (I had to bore a hole for mine)
- Plan out how you want it to operate, mine ended up way more complex. I had to install a keypad, safety photo eye, safety metal detection loop, a free exit loop (detects cars exiting). All of these cost extra.
- I ended up going with aluminum gates to save on weight. Posts are 4x4 steel set 4' down in concrete. I had to weld gussets on the hinges to prevent bending / flexing. I ended up using an ameristar gate, expensive, but great quality
- If you do columns around the gate I'd make the columns a bit taller than the gate VS level or shorter (huge difference in looks - I had to add height to my columns)
- It's shockingly expensive. Doing it over I may have not done all the automation, costs were over $16k and it turns out virtually no one turns around in my drive now when the gate is open, just a gate deters them even if it's not closed.