This is a tough question to answer as both play an integral role in how we function in our everyday life.
Behaviors are typically in response to gain something (reaction, physical item, or a desired outcome). There is usually an antecedent that precedes the behavior (being told “no, not right now, stop”, etc.), and finally the consequence (time out, quiet time, removal of desired item). Behaviors can also be considered a way to gain attention from another individual in order to get the desired response which is more attention which can be either positive or negative. For example: a child wants to stay at the playground with his or her friends. An adult tells them no, which results in kicking and screaming, ignoring adult direction, fleeing or attempting to return to the playground. These behaviors are communicative to the adult that they do not want to leave the playground. Tips to reduce behaviors or promote positive transitions may include: giving a verbal countdown, use of a visual timer, concrete directions (pick one more slide to go down and then we will go get our snack).
Sensory concerns are usually consistent throughout environments: typically, noisy environments with several people, visual and even olfactory input. Overwhelming sensory environments on a daily basis could include examples such as: Bath and Body Works with overwhelming olfactory/smell input; malls with overwhelming olfactory/smell/visual input; arcades with overwhelming visual/auditory input. In response to overwhelming environments, you may see children avoid or attempt to flee the environment, ignore adult direction, drop to the ground, attempting to hide in the corner or seek proprioceptive input from an adult (intense hugs from adult. Tips to reduce behaviors and promote positive responses include: calming breaks (finding calm corner in location where you are, take a break and go outside to sit in the car for a few minutes, bring headphones or calming music to block out miscellaneous noise, giving child autonomy to decide when they are ready to reenter, etc.