There are only three Major Scales, and the onlt differences between them involve the 4th and 5th degrees. If you look at them this way, it allows you to realize that they are more similar than different. Which scale you use is then dictated by your taste and what the tune or style of music calls for.

The most common Major Scale is also known as the Ionian Mode (why are we speaking Greek?). It looks like this:

This is the scale most closely associated with a Major 7 chord and it's relatives, Maj 6, Maj 9, Maj 6/9, etc. Use this Major Scale over Major chords when playing in strongly key oriented tunes such as Rhythm Changes and whenever the chord progression resolves stongly to a Major chord. With this scale, the 4th degree is not usable a s a point of rest or emphasis because it makes babies cry and will annoy your fellow musicians if you play it. Really.

To get around this problem, raise the 4th degree by a half step, which is known as the Lydian Mode (thanks Lydia, whoever you are). It looks like this:

The 4th degree can now be used as a point of rest. This scale is closely associated with the Maj7#4, Maj7#11, Maj7+4, etc chords. Some folks write it as flat 5, which to me is misleading, since the scale has a natural 5. Hey, a guy (or gal) can rant every once in a while.

The Maj7+4 Scale is more commonly used when the Major Chord (including plain old Maj7) lasts longer than say, one measure (unless the tempo is slow). You might not use it as much on Rhythm Changes as you would on a Wayne Shorter or Joe Henderson tune. A good way to get the Lydian sound is to outline the major triad built on the second degree of the scale (check out example 2 of Lesson 5)