I hate to sound like a "smart-***" but it really doesn't matter. All of the shells (Remington and otherwise) "go bang" and break targets IF you do your part. The difference in 7 1/2 and 8 shot is very small and there is a trade off of pellet count vs. retained energy. Generally for skeet and 16-yard-line trap 8's will break anything. For handicap trap (because of distance) and sporting clays (because of hard targets like the battue and rabbit) I prefer 7 1/2.
Gun Clubs are just fine, except the "old stock" currently being phased out that had primers that were hards as rocks. They are being replaced with the brass-cupped STS primers because of so many complaints. Since the Gun Clubs tend to use lesser-grades of shot (softer, more lead, less antimony) I generally prefer the 7 1/2's, but the 8's work just as well.
The STS's is a great shell - not much else needs to be said. I use 8's mostly, except handicap I use 7 1/2's from the 25 yard line.
Not bragging, but I've run 100 with both in trap, so either one will fit your need just fine. Whichever you can get cheaper is great.
Usually the Gun Clubs will be cheapest, but Remington has been offering $2 a box rebates on STS/Nitros....I saw dealers at some shoots selling these for $67.99 per case of 10, ($6.79 a box) , -$20 would bring the cost to $4.79/box $47.99/case for STS/Nitros, and I haven't seen Gun Clubs that cheap in a while!!!!!