Brainy

Fits when ability is truly exceptional rather than simply strong

Careful Calling every capable person brilliant weakens the praise and overstates the evidence.

Fits when quick understanding or an inventive solution stands out

Careful Clever may praise one trick without claiming deep intellectual strength.

Fits when alert perception and fast judgment are central

Careful Sharp says little about accumulated knowledge or scholarly interests.

Fits when direct, familiar praise fits the audience

Careful Smart can also mean stylish, so the sentence may need more context.

Fits when intelligence is paired with promise, especially in a young person

Careful Bright is gentler and does not carry brainy's enthusiastically academic flavor.

Fits when fast verbal or mental responses deserve attention

Careful A slow, profound thinker can be brainy without being quick-witted.

Fits when a neutral, respectful judgment of mental ability is needed

Careful Intelligent is broader and less playful than brainy.

Fits when a person or work appeals primarily to intellect

Careful Cerebral can imply emotional distance and is not a simple compliment for intelligence.