I think the full speed level, but focusing on power this time. Vegeta saw how he was outmatched in speed and Freeza demonstrated his power superiority when Vegeta decided to unleash the super attack, which forced him to get a little serious in power and show speed wasn't the only thing he got Vegeta heavily outclassed.
Then vs Goku, he likely used the initial level when fighting the other warriors imo and went back to the schooling Vegeta level in their warming up... And then increased it even more when fighting no hands, to which may have been fighting base Goku at full power, which I'm nowadays tending to go with the colored manga depicting that as full power base Goku.
I think it's similar to Cell. Freeza like Cell noticed Vegeta's speed and increased it firstly. Then upon noticing Vegeta also had that huge power, decided to bring the power up to the speed increase, like Cell presumably did once seeing Gohan wasn't just quick but also tough. The fact the warriors were in disbelief at Freeza kicking that blast away, with Goku noticing how it was strange Vegeta's power was dropping that quickly also lends credence to the initial true form Freeza before getting a little serious not being out of Vegeta's realm to the point of making his power take a huge dip that quickly. I'd say Vegeta is pretty close to initial Freeza, may be like 90% ++ power and be able to put up a good fight... Which explains his lack of total confidence, but also explains the fact he didn't seem in denial when observing Freeza's movements and only showed denial signs when he saw Freeza's more serious speed and the power when kicking the blast. Firstly it was the denial of screaming he was a SSJ and then the total lack of will to fight.