更 and 最: even more, the most
副词 / adverbs (程度)
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
更 + Adj / 最 + Adj
更 (gèng) = "even more": it compares with something that already has the quality. 这个很好，那个更好 (this one's good, that one's even better).
最 (zuì) = "the most": superlative. 这是最便宜的 (this is the cheapest).
With 比 you can say A 比 B 更 Adj (but never 很).
Examples
这个颜色更好看。
Zhège yánsè gèng hǎokàn.This colour looks even better.
三个手机里，这个最便宜。
Sān ge shǒujī li, zhège zuì piányi.Of the three phones, this one is the cheapest.
坐高铁比坐飞机更方便。
Zuò gāotiě bǐ zuò fēijī gèng fāngbiàn.The high-speed train is even more convenient than flying.
你最喜欢哪一个？
Nǐ zuì xǐhuan nǎ yí ge?Which one do you like best?
Common mistakes
✗ 更很好 → ✓ 更好.
✗ 这个是更便宜的三个里 → ✓ 三个里这个最便宜 (superlative = 最).