The 6 best globular clusters of the whole sky are here presented. This comparison is obtained with the same telescope and camera, shown at the same image scale. Processing is nearly the same for each image, even if a small individual optimization was necessary.
For me, living in the Northern hemisphere, it is a bit sad to notice that 5 o 6 have negative declination, and that the best 3 never rise on my horizon in Italy.

Omega Centauri is by far the largest of all, and also the brightest, easily visible to the naked eye.
47 Tucanae is a spectacular subject, expecially in the binoculars, where I can see two globulars, one inside the other (due to the high concentration in the middle).
NGC 6752 is similar to M13, but larger and brighter.
M22 is spectacular for the huge carpet of neighboring stars.
M4 is near one of the most spectacular regions of the sky, the Antares nebulae region.

For a comparison of only Omega Cen and M13, look at "Comparison of Omega Centauri and M13".

Here is a table listing the above globulars.

Ordered by magnitude
	Mag	Size [']	Dist [kly]	Const	Dec
Om Cen	3.9	36.3	15.8	Cen	-47
47 Tuc	4.9	30	16.7	Tuc	-72
NGC6752	5.4	20.4	13	Pav	-60
M13	5.8	20	22.2	Her	36
M22	6.2	32	10.6	Sgr	-24
M4	7.2	18	7.2	Sco	-27
Ordered by size
	Mag	Size [']	Dist [kly]	Const	Dec
Om Cen	3.9	36.3	15.8	Cen	-47
M22	6.2	32	10.6	Sgr	-24
47 Tuc	4.9	30	16.7	Tuc	-72
NGC6752	5.4	20.4	13	Pav	-60
M13	5.8	20	22.2	Her	36
M4	7.2	18	7.2	Sco	-27