best vs first up

best

• To the most advantage; with the most success, cause, profit, benefit, or propriety. 

• Most; largest. 

• Most superior; most favorable. 

• Had best. 

• To surpass in skill or achievement. 

• To beat in a contest. 

• The person (or persons; or thing or things) that is (are) most excellent. 

• The supreme effort one can make, or has made. 

• One's best behavior. 

first up

• Firstly; before anything else.