There are two main editions of Peter Pan illustrated by Rackham. The first edition, published in 1906 w/ 50 tipped-in plates mounted on heavy green art paper w/ tissue guards and a new edition in 1912 an addition of one new illustration.

There are multiple reprints between 1906-1912. The early ones are the same as the 1st w/ similar quality reproduction. Later ones 1910+ only have 16 plates, not tipped-in, yellow borders, the quality is poor, faded colours, lack of details, etc.

True first is quite expensive and hard to find in VG condition where the plates are in perfect condition. The problem with tipped-in plates is the plates are mounted/glued on the top edge only and prone to have corners creases at the bottom corners where they're loose.

The best ones are the two main editions stated above. If you can find early reprints in 1907, they are a bit "cheaper" ($300-$700). Not sure what your budget is, but I'd suggest you to save and get a first or early reprints w/ 50 tipped-in plates. I collect Rackham and have all of his most important works and that's my recommendation. There is no "good" edition after the early reprints 1907-1909. All suffer from poor quality of reproduction w/ the exception of the 1912 "new" edition.