Note: I will be including support in these power rankings so it's not just who I think are idvually the best players. As another preface I have seen less of Fakes, elodin, and Mdragon's GSC than the other players on this list so my rankings for them are more likely to be off.
1. choolio
Choolio is likely at worse a top 3 player in this year's GSC pool, and would obviously be frontrunner in the pool no matter what. However the Wolfpack support in my mind pushes the slot to the top. Having Fear, D4 and coco support is insane, and i look forward to seeing what teams get brought from the Wolfpack this year.
2. MDragon
Like I said in the preface I haven't watched enough Mdragon to feel like I'm truly giving an accurate ranking, but with such a legendary GSC player and d0nut/Garay Oak support its hard to imagine M Dragon not putting up a good record.
3. Rubyblood
Ruby has had potentially the best year of any of this year's SPL players (besides maybe underlying/fluid), winning the circuit, winter seasonal, and putting up top 8 result in invitational. I rate Ruby lower than the 2 above him mainly due to weaker support relative to the Wolfpack/Classiest.
------- (I think the top 3 here has a bit of a clear gap over the next group of people)
4. Zokuru
Zok always has the potential to perform well in team tours especially with mangers he gets along with. Gorgie and Zok building together can give rise to some great new teams and have worked together in the past. The rest of the support on the team for GSC also seems solid so hopefully they can prevent to "unique" of loads.
5. Underlying/Fluid
Underlying has had quite a good year and has Vileman support for this SPL. Underlying's GSCPL, GC, and Invitational performances show his consistency against top players (although he was a lucky .... in GSCPL). There are no clear flaws when he plays, but it will be intresting how his consistent style translates against the SPL pool.
6. Jester
Very solid player, but Jester hasn't played too much GSC this year to my knowledge. It's also uncertain to me, how strong his GSC support will be, BlazingDark seems like good support and obviously ABR is very good at GSC but ABR's time is likely going to spread across many generations.
7. Aminita
Aminita has had a very solid year, putting up very good performances in the Winter Seasonal, and GSCPL. Aminita is a very creative builder (maybe too creative) and paired with Conflict is sure to be bringing good teams and to be well prepared for most opponents on this list. (Switched up on the day ones)
8. Fakes
There is a high likelihood I'm incorrect in this ranking, as many people better than me rate Fakes highly. The only GSC of his I have seen this year was from classic, where his play seems weaker than what I'd expect from those listed above him on this list. With more prep and focusing just on GSC, his play is likely to be on a much higher level for SPL though. Another thing lowering Fakes on this PR compared to those above him is the GSC support, Kingler/prinz are not GSC mains or builders for the tier as far as I know.
9. Ombrarch
I believe Ombrarch is on a relatively similar level of GSC as those ranked 4-8, but his support seems truly lacking compared to what others on this list have. I assume they have a GSC helper in their server but even that likely cannot be better support than Flict/Vileman/Gorgie/ABR unless they managed to convince Siatam, Soup or someone of that caliber to join the server.
10. Elodin
Elodin is clearly a top mons player in general, but his recent GSC results have been lacking. During classic this some of his play/teams brought seemed suspect. It is hard to rank elodin above Ombrach considering lack of general GSC play, and overall results this year, but as very good general mons player with a increased commitment to GSC his results could definitely go against what I would expect at the start of the season.