You can only get knocked up once every 10 seconds from Rek'Sai, and that isn't reduced by CDR.
Blitz's rank 1 power fist is only on a 9 second cooldown and goes down by 1 every level, and is reduced by CDR. Cho'Gath's AoE knockup radius is WAY bigger than Rek'Sai's, that's on a 9 sec cooldown, reduceable by CDR.
But Blitz has to land a pull!" you might say, or, "Cho'Gath can't get close enough to Rupture!" How about Maokai's Arcane Shift: 6 second cooldown, reduced by CDR. Combined with a point-and-click gap-closer that makes the knockup a guarantee.
Other champs with knock ups on cooldowns lower than Rek'Sai's, either after some leveling, a little CDR, or immediately: Singed flip, Thresh Flay, Sion q, Janna tornado, Jarvan dragon strike to standard, Volibear toss, Xin's 3-talon strike.
Why are you specifically pinpointing the synergy with Rek'Sai? Xin is better at it: he's got a 5 second knockup with a cooldown that gets lower with every auto, and a point-and-click gap closer that gets him right to you. At least Rek'Sai's gap closer requires some finesse to get where you want to be properly; you can't just point and click a champ and be underneath them with Rek'Sai.