Comparisons

Comparisons can be divided into two types: comparatives, which pit two things against each other, and superlatives, which describe one thing as beyond everything else in its category.

Comparatives

toki pona doesn't have a specific grammatical construction for comparatives, but there are nonetheless multiple ways to express them:

Separate the claim into two sentences with an implied connection:
poki mi li lili. sike sina li suli.

My bag is small. Your ball is big.

poki mi li suli (lili). sike sina li suli mute.

My bag is (a bit) big. Your ball is very big.
Do the above, but make the connection explicit with taso:
poki mi li lili, taso sike sina li suli.

My bag is small, but your ball is big.
Use la to make the magnitude of one claim relative to the other subject:
poki mi la sike sina li suli.

In terms of my bag, your ball is big.
Similarly, use tawa to put the claim "in the perspective" of another:
sike sina li suli tawa poki mi.

Your ball is big to my bag.
Use a superlative with a limited scope:
poki mi en sike sina la sike li suli nanpa wan.

In terms of my bag and your ball, the ball is number one in bigness.

poki mi anu sike sina la sike li suli mute.

In terms of my bag or your ball, the ball is very big.

With any of these methods, you can either:

Compare the objects:
poki mi la poki sina li loje mute.

In terms of my bag, your bag is very red.
Or compare the quality itself:
loje pi poki mi la loje pi poki sina li suli.

In terms of my bag's redness, your bag's redness is big.

A fuller list (albeit with some very weird examples) can be found here, courtesy of /u/forthentwice.

Superlatives

Superlatives are even simpler:

Use nanpa wan:
poki sina li suli nanpa wan.

Your bag is number one in bigness.
Intensify the claim:
poki sina li suli mute.

Your bag is very big.
Use a comparative (see section 1), with the other argument being everything that is relevant:
poki sina li suli. poki ante ale li lili.

Your bag is big. All other bags are small.