• Formula: subject + adjective + 乃. Used when the object of comparison is not explicit.

佢高乃 He is taller
苹果好吃乃 Apples are tastier (Cantonese: 苹果好食啲)

• Formula: subject + adjective + 过 + object. Used when the object of comparison is explicit.

佢高过我. He is taller than me.
苹果好吃过橙. Apples are tastier than oranges.

• Formula: subject + 比 + object + adjective. Used when the object of comparison is explicit. This is more formal and likely came from Mandarin.

佢比我高. He is taller than me.
苹果比橙好吃. Apples are tastier than oranges.

• Formula: subject + 冇 + (object) + 该^kɔi21 + adjective.

佢冇(我)该高. He is not as tall (as me).
苹果冇(橙)该好吃. Apples are not as tasty (as oranges).

• Formula: subject + 有 + (object) + 该^kɔi21 + adjective. This is the opposite (with 有 replacing 冇) of the previous structure. However, the objective is to stress emphasis, and this form is not used to make a  plain statement.

佢有(我)该高! He IS as tall (as me)!
苹果有(橙)该好吃! Apples ARE as tasty (as oranges)!

• Formula: subject + 同 +object, 同埋^mɔi22 + 该^kɔi21 + adjective. 一样 same, 差唔多 about the same, etc. can be used instead of 同埋.

佢同我,同埋该高. He is as tall as me (He and I are of the same height).
苹果同橙,同埋该好吃. Apples are as tasty as oranges.

• Formula: subject + 同 +object, who/which + specifier/unit + adjective + 乃?

佢同我, 乃个高乃(or 谁高乃)? He and I, who is taller?
苹果同橙,乃样好吃乃?. Apples and oranges, which are tastier?

The above construction can be modified by degree modifiers: 啲多[nit55 ɔ215] a tiny bit, 少少[siau55 siau55] a little bit, 几多[gi55 ɔ335] quite a bit, 好多[hɔu55 ɔ335] a lot, etc.

佢高啲多. He is a tiny bit taller.
佢高过我少少. He is a little bit taller than me.
苹果好吃过橙几多. Apples are quite a bit tastier than oranges.
苹果比橙好吃好多. Apples are much tastier than oranges.

The superlative is 至 or 最. 至 is an older expression and is being replaced by 最, part of the processing of converging toward a common (usually Mandarin) vocabulary among the various Chinese dialects¹.

佢至高(咯啰). He is the tallest.
苹果最好吃(咯啰). Apples are the tastiest.

More examples:

你个女靓乃. Your daughter is prettier.
今日凉过昨日. Today is cooler than yesterday.
华仔乃头毛挛过华女(乃头毛). Wah the Boy's hair is curlier than Wah the Girl's (hair).
你比我怕丑十倍. You are ten times shyer than me.
佢叻过我好多. He's much smarter than me.
飞机快过火车不知几多! Airplane is so much faster than train! 你走快乃毋我走快乃啊? You run faster, or I run faster? 我一啲都冇佢该恶! I'm absolutely not as mean as he! 生活比以前好些少. Live is a little bit better than before.