There's more to the various Gerry & the Pacemakers `Best of' compilations than a mere variation in track count and/or choice.
The disc `The Best of Gerry & the Pacemakers: The Definitive Collection', released in 1991, offers most of its 25 tracks in stereo. The remastering (and in some cases remixing) has been very carefully done at Abbey Road Studios, where most of the tracks were recorded. The sound is very good, although some may argue it is not the original sound of the hits, as all singles were originally only issued in mono. Some stereo versions are quite primitive, as the tracks were recorded on 2-track: one for the backing track, one for vocals, just like the earliest Beatles recordings, but the people at Abbey Road managed to 'open' the sound. This CD also offers `Hello Little Girl', never before released - probably because The Fourmost had their recording released first (which was a minor hit).
Another good compilation is `Gerry & the Pacemakers at Abbey Road: 1963-1966': this offers 28 tracks (comprising the 25 of the aforementioned CD), but they are all in mono. This CD has been denoised, which, if properly done, will not degenerate the sound, but may affect the way you experience it. I found the sound to be a bit sharper, but not annoying. The booklet is very well done, detailing the band's history, and a bit of the history of Abbey Road studio's. This disc has been re-issued as `Essential', but alas without the informative booklet.
Recently the budget 2CD `The Best Of G&TP' has been released, offering 40 tracks, which is excellent value for money, but it leaves out some of the tracks which are on the other CD's, offering more album tracks like rock'n'roll and oldies covers.
All in all, I think that the choice is yours. If you come across a cheap compilation CD, other than the ones mentioned here, I recommend you listen to them first for sound quality - try before you buy!