The very bottom one could possibly get scratched easier, but never found that to be an issue. The pack side is not very related to the number of defective discs, so the 100 pack is usually the better value. The brand itself does not make much of a difference either. The country of origin (Made In ***) makes the big difference and if you want all good discs, pay the double+price for made in japan Taiyo Yuden. I prefer the Taiwan made over the mainland China ones. Made in India were ok also. Most of the China made is about the same. You know the good from the bad by bad being the thinner coated surface, or if the end that blanks out burns fast. (If 4.5GB used, the edge could blank fast or slow. Slow is a better quality disk). Can also improve by putting less data on a disc. The edges have thinner coating and scratch easier. 100 or 25 is irrelevent. Country of origin and how much data and to some extent, after you buy one you know if it is any good on the first disc.
It is normally more cost-effective to buy them in by the 100's, the only advice I would give to you is that you keep the pack upright and try not to move it, otherwise it could possibly (but rarely) scratch the bottom ones. In general, they tend to be better made nowadays than what they were.
Hope this helps.