The correct word to complete the sentence is "affordable."

So, the full sentence would be:

"It is often more affordable to live in the suburb than in the city."

This means that living in the suburbs tends to cost less than living in the city, particularly in terms of housing, rent, and other expenses.

The sentence you're looking for can be completed with a word like "affordable" or "peaceful."

For example:

"It is often more affordable to live in the suburb than in the city."
"It is often more peaceful to live in the suburb than in the city."
Depending on the context, other suitable words could also include "spacious," "convenient," or "comfortable." If you have a specific aspect in mind, please let me know!