I think by this point the Kings Apartment tour may be booked.. but I have only read satisfied reviews of it.. so if its available it is a good option for you.
I think visiting the gardens then doing the tour is a good option.. and even if you can't get on the tour.. you could still visit the gardens and visit the palace after about 3. or 3.30 as most of the tour buses are gone by then so lines are not as horrendous.
The Museum Pass does allow you to skip the Ticket line.. but not the security line for the palace.. .. and the security line can be very long. We arrived pass in hand about 10.30 in am.. big mistake as we had to wait at least another 45 minutes in hot sun to get through security.. doing the gardens first makes good sense as once my dd and I slept in and didn't arrive at Versailles till after 1.30 and there was almost no line for security ( that was almost 5 years ago though. lines are worse now, hence try after 3.. )
The palace will be crowded,, and its great to see,, but really for most the highlights of Versailles are enjoying the grounds ,, and getting out to Marie Antionettes Hamlet and the Grand and Petit Trianons.. so do grab the little trolley ( extra fee) because just walking to those parts of the estate can take a half hour.. one way! Fine for those with time.. but you are really pushing it with a 1/2 day to see everything.
