"Top 100" refers to a specific list of Morgan varieties grouped under that title. It has limited relation to popularity, value, availability or general interest.
"1887/6" refers to the overdate and VAM-2 is the specific variety. Here's the description copied from VAMWorld:
1887-P VAM-2 7/6 Overdate
Discovered by Ted Clark, November 1971.
This coin is a Top 100 Morgan VAM. 2 III2 2 C3a (7/6) (189) I-5 R-4 Obverse III2 2 - 7 repunched over 6 in date. The bottom loop of the 6 shows as a long curved line starting up slightly from the lower right bottom of the 7 and extending upwards one-third the digit height. On the left side of the stem, a short spike slants upwards at a point one-third the way up on the stem height. A short vertical spike shows at the very top of the 7 crossbar in the middle. A short spike also slants upwards from the middle right side of the crossbar.
Comments: 1. 1887 VAM-2 7/6 overdate. This variety is one of the Morgan VAMs recognized and priced in the Red Book, crossing over into many mainstream collections. If you examine the last digit of the date, a 7, the remnants of a 6 can be seen to the lower right. 2. Horizontal scratch in front of the eye as a Pick Up Point from Vampicker. See additional photos below