When i listen to guys like Gary Moore, Adrian Smith, Zakk Wylde i hear a really wide, moderate speed vibrato. I listen to kirk hammet's vibrato and i hear a very narrow and extremely fast vibrato that sounds like a bee trapped in a beer can.

I know everyone will have different tastes when it comes to vibrato but is it a case of the wider the vibrato the better ?

I know most players will have a number of vibrato's and will adjust the tempo of the vibrato to the song.
Good vibrato is about having the control to return to the pitch you started from each time you bend. So, for example, if you start on an A and use tone-wide vibrato then you bend up to the B and back down to the A each time.

Most people seem to also prefer a slower, wider vibrato as well but that is personal taste, the important thing is the regular bend out to the same pitch and return to the original.
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wider isnt alway better
maybe it can be if your trying to really emphasize a note or a bend but sometimes very subtl vibrato is what the song or passege needs
...so i think controlled vibrato is better (also if its in tune and in itme it usually sounds betterto me)
Practising vibrato in time is always very good. I think there was an interview with Chris Broderick on the UG homepage very recently, and he talked about how learning violin and practising his vibratos with a metronome, as quavers, semiquavers, triplet quavers, and all that, really helped give him a damn good vibrato.
To get that vibrato, all u rly need to do is just move your finger rly fast back and forth across the fret youre playing on, I kno wat u mean
Vibrato is like any other technique - there's a time and place to go really fast, there's a time and place to go really slow, and there are times and places for everything in between.

I personally prefer a more rapid finger vibrato similar to what a violinist uses, since I played violin before I started guitar. However, I like to use a wider, circular motion combining a bluesman's vibrato with the classical motion, something which Steve Vai has recommended in some of his videos.
Moderation is key. Too much vibrato and it sounds like a warbling out of tune guitar. on the lower frets (1-5) I suggest using up and down vibrato ( slightly bending) make sure you move the same distance away from the center on either side. (not farher bent up than down)
On the upper frets (5and up) use the side to side, just slightly move your wrist side to side and DON'T slide your finger. I advise to use these two methods for how the string tension is. Side to side vibrato isn't as effective lower because it adds less vibrato because of the higher tension. And up and down bending is a bit too much on the higher/ less tension portions of your guitar. (it has a tendency of over-bending) unless you're looking for that wide extreme blues-like vibrato, which is good and fun in some cases.

Hope this helps, and rock on brother!