I'm not in top 25 but got a lot of matches, i'm just not tryharding the 'ladder' cause i hate the ladder 'the more you play, even if you'renot that good, you'll climb' since top 26 got nothing but can beat the 25/24/23th etc..  :Crazy:  
 last season 
 current one   
So here my top tier list atm :   
If their ivs + nature are good, you can add legends such as Mew and Jirachi now. So it's 2 (celebi is harder to play, but very good too, i let him apart) 
Edit : you wrote in the grass sorry (but they can be played in pvp so :s )   
Not a specific order but here are 18 others i always see in pvp : 
-Sableye 
-Togekiss 
-Slowbro 
-Talonflame (heabutt counts, right ?) and his friend 
-Staraptor 
-Breloom 
-Scizor 
-Magnezone 
-Excadrill Sand rush, with 
-Hippo or 
-Tyra 
-Lanturn 
-Cloyster 
-Blissey 
-Ferrothorn 
-Azumarill 
-Garchomp 
-Dragonite 
-Starmie 
-Venusaur   
Offlist but good : 
-Blaziken if speed boost coded (but never saw one) 
-Clefable when magic guard coded 
-Skarmory 
-Machamp 
-Conkeldurr 
-Gyarados 
-Gengar   
 :Angel: