A comparison may be expressed either with genitive case, or with the conjunction чем meaning "than" with no difference in meaning :

Сестра красивее брата. Сестра красивее, чем брат.

In spoken Russian I prefer a short form when possible, but both are widely used.I said "when possible" because if I use менее +adjective, I say чем.

With the compound form, the construction with чем should be used, you can't use genitive in this case:

Они – двойняшки, но сестра более активная, чем брат.

The construction with чем should be used with parts of speech which are not declined or with prepositions:

Сегодня день теплее, чем вчера. Мороженое с клубникой вкуснее, чем с вишней.

A comparison can be expressed either with genitive case, or with the conjunction чем meaning "than" with no difference in meaning :

Сестра красивее брата. Сестра красивее, чем брат.

In spoken Russian I prefer a short form when possible, but both are widely used.I said "when possible" because if I use менее +adjective, I say чем.

With the compound form (более,менее + adjective), the variant with чем should be used, you can't use genitive in this case:

Они – двойняшки, но сестра более активная, чем брат.

The construction with чем should be used with parts of speech which are not declined or with prepositions:

Сегодня день теплее, чем вчера. Мороженое с клубникой вкуснее, чем с вишней.

A comparison may be expressed either with genitive case, or with the conjunction чем meaning "than" with no difference in meaning :

Сестра красивее брата. Сестра красивее, чем брат.

In spoken Russian I prefer a short form when possible, but both are widely used.

With the compound form, the construction with чем should be used, you can't use genitive in this case:

Они – двойняшки, но сестра более активная, чем брат.

The construction with чем should be used with parts of speech which are not declined or with prepositions:

Сегодня день теплее, чем вчера. Мороженое с клубникой вкуснее, чем с вишней.

A comparison may be expressed either with genitive case, or with the conjunction чем meaning "than" with no difference in meaning :

Сестра красивее брата. Сестра красивее, чем брат.

In spoken Russian I prefer a short form when possible, but both are widely used.I said "when possible" because if I use менее +adjective, I say чем.

With the compound form, the construction with чем should be used, you can't use genitive in this case:

Они – двойняшки, но сестра более активная, чем брат.

The construction with чем should be used with parts of speech which are not declined or with prepositions:

Сегодня день теплее, чем вчера. Мороженое с клубникой вкуснее, чем с вишней.