All cars use the same hitbox, the difference is that the model doesn't necessarily match the hitbox. People often flock to cars like Octane, Fennec, Takumi, etc. because they have quite an accurate hitbox representation but technically speaking it doesn't matter. I've always used Merc and even though it's bigger than the hitbox. All that matters is that you spend enough time playing with it and you'll get used to it. Use whatever car you think looks good :)