There's not only one type of adamantium but many and that happens for vibranium too.
Wakanda's vibranium, Antarctic Vibranium, Reverbium...there's even Living Vibranium ( a sentient version of it) all with different characteristics.
For example Wakanda's absorbs kinetic energy making it more resistant by storing that energy in the molecular bonds ( until it excedes a limit and it explodes) while Antarctic's have the opposite behavior: instead of absorb it emmits kinetic energy breaking the molecular bonds of the surronding material.
So your question can not be answered precisely because we would have to determine how much kinetic energy is the vibranium (Wakanda's) storing. If we go to the limit ( one punch left to explode) there's not much difference from Adamantium to Vibranium but of course...you have a bomb about to explode in your hands!! That is usually considered a handicap.
On the other side ( this is Marvel abandon any hope of coherence or hard scif-fi) Adamantium has a relative low melting point of 3000ºC - 5500ºF ( that is high for a metal but low for an universe with living gods) so if you are asking (again)....wait ....wait....why the fuck does Ultron ( the comic's one) even exist? If he melts at 3KºC he should be easy target for Thor - lightning excedes that temperature by an hilarious marging - or Human Torch - up to 1 Million ºF.....well,as stated,this is marvel...abandon any hope for coherence.
So what's more resistant? Resistant to what?
Kinetic energy? Adamantium....it's basically indestructible by this mean but the downside is that you are punched by Hulk on your adamantium shield and you are sent 200 m in the air while a vibranium one absorbs the punch.
Thermal energy? Vibranium...it absorbs the energy instead of melting at 3000ºC but the downside is sooner or later you are gonna exceed its maximum capacity and it will explode.
If you are thinking about the MCU I have no doubt...Adamantium will be the king. Why? Because it's still not present and cinema has this trend of "Bigger,Faster,Stronger..." so you will end up in a Banner or a RiRi Williams or a Reed Richards yelling in awe:"This material is stronger that Vibranium!!! I can not believe it!!" /pikachuface