I think Suicune > Skarm.
Suicune vs Starm for #5 I dont really know, any of them could easily be #5.
They are pretty similar in all gens (except ADV where Suicune is much better), but Suicune didnt exist in RBY, while Starm was top 10.
Some candidates for #8, #9 and #10:
Blissey is not very good in GSC, but it has a great impact in ADV and DP.
Celebi is top 3 in ADV, and very good in DP
Vaporeon is a big threat in GSC, and a very good bulky water in ADV/DP, giving Wish support too, but it sucks in RBY.
Jolteon is decent in RBY, a good agility passer in GSC, and decent in ADV and DP.
Dragonite is excellent in RBY (wrap), a good mixed sweeper in GSC, its decent in ADV and a monster in DP (especially after mence ban). It could easily be at least top 10.
Heracross is decent in GSC and DP, and a huge threat in ADV.
Forretress is a good option for a spiker + spinner in GSC; in ADV although it not a good spinner (unless it has pursuit support), it can spike and spin, and it has useful resistances; in DP it can set up all the hazards, and it can also spin.
Cloyster is a great option in RBY vs snorlax/tauros and can clamp and explode; in GSC it's the best spiker, and has a good explosion (usually removing things like Starm/Lax), and can also spin; in ADV it is the only spiker in OU/BL that isnt trapped by Magne. It sucks in DP though.
Machamp is not good in RBY, but its a huge threat in GSC and DP, and it can also be useful in ADV.
Raikou is top 3 in GSC, a huge threat in ADV (it fears Duggy though), and it can also be dangerous in DP.
Salamence didnt exist in GSC and RBY, but it was probably top 5/6 in ADV, and it was considered broken in DP. Maybe not top 10 because being present in 2 gens (but if we consider Celebi as Uber in GSC, Celebi is then in a similar case)