-Sanji is faster than Zoro in base and even more so in Raid Suit but loses in the strength department.
-Raid Suit gives Sanji more speed, strength and durability. It also has stealth and a shield for his cape.
-Sanji has better Observation Haki and we have yet to see Sanji use Armament Haki.
-Sanji’s strongest kick so far is his “Crosse Strike” which he used against Big Mom to save Reiju.
-Sanji has had a fight with stronger people than Zoro has so far. Vergo, Page One, and a clash against Doflamingo. With his fight against Vergo he cracked his leg and if they continued fighting, he would’ve ended up breaking his leg. And against Page One he overwhelmed him with his speed and stealth, but he did almost no visible damage. He has had other fights, but these are his strongest opponents so far.
-Zoro in base form is stronger and has more stamina and durability than Sanji though only if Sanji doesn’t use the Raid Suit.
-Zoro now has Enma which powers up the amount of haki he can release and the overall control of haki throughout his body.
-Zoro has better Armament Haki and decent but worse Observation Haki than Sanji.
-Zoro’s strongest sword technique so far is his “Three Sword Style Secret Technique: The Billion-fold World Trichiliocosm” which was used against Pica.
-Zoro has had a fight with Pica and Killer as his strongest fights so far. He has also had a clash against Admiral Fujitora and Kyoshiro. He washed Pica easily in the fight though he did use his strongest currently known attack in the fight. Also, he fought Killer while Killer was in a weak state and they still ended up having a draw. Although they both didn’t have all their main weapons and Zoro was also fighting Gyukimaru at the start, the fight still ended with them both one shotting each other. This was pretty surprising considering the amount of damage Zoro can usually take. He has had other fights, but these are his strongest fights, clashes so far.
They both have a wide verity of techniques and skills they can use during the fight. They both also have a temporary transformable state that they can use. These are Sanji with his “Hell’s Memories” and Zoro with his “Nine Sword Style: Asura”. Sanji used this against Wadatsumi in Fishman Island where he ignites his whole body on fire and his kicks can light his target on fire when he kicks them. Zoro used Asura against Kaku of CP9 in the pre time skip and against a Pacifista PX-4 during the Sabaody Archipelago Arc.
From what we have seen of these temporary transformable states is that they can only use one powered up attack and then the form ends. Maybe later these will be actual forms that they can keep active for long periods of time just like Luffy’s Gear Second.
This is all I have to say on the matter of the Sanji vs Zoro topic. No head canon or random stuff like we haven’t seen Zoro or Sanji at full power yet, etc..