非常 / 特别 / 比较【fēicháng / tèbié / bǐjiào】

These go where 很 goes, in front of the adjective, and unlike 很 they carry real weight.

• 比较 – relatively, fairly. Weaker than 很.
• 很 – the neutral filler.
• 挺…的 – pretty, quite. Casual, and usually closed with 的.
• 特别 – especially, particularly.
• 非常 – extremely.

比较 hedges

比较 is how a speaker avoids committing. 这个比较贵 is a soft way of saying something costs too much, and it does not need a second thing to compare against.

挺 takes 的

Leaving the 的 off is possible but sounds clipped.

特别 also means "special"

As an adjective it means particular or unusual: 一个特别的地方. As a degree adverb it means "especially".

They do not stack

One degree adverb per adjective. fēi cháng非常hěn很hǎo好 is wrong.

None of them fit a 比 sentence

A comparison takes only 更 and 还. tā他Bǐ比wǒ我fēi cháng非常Gāo高 is wrong.