Are there any indications that filling under either of these eligibility criteria is easier, smoother, or faster?

Assuming one satisfied the continuous residence requirement as well as the physical residence requirement, N-400s based on 5 years of lawful permanent residency are easier than N-400s based on marriage processed, because one doesn't have to prove the genuineness of the marriage. The USCIS doesn't release statistics on which one is faster to process.

Are there any indications that filling under either of these eligibility criteria is easier, smoother, or faster?

Assuming one satisfied the continuous residence requirement as well as the physical residence requirement, N-400s based on 5 years of lawful permanent residency are easier than N-400s based on marriage processed, because one doesn't have to prove the genuineness of the marriage. 

The USCIS doesn't release statistics on which one is faster to process. However, this spreadsheet contains >200 application timelines for Seattle that you can use to see whether marriage-based N-400 applications are faster.

Are there any indications that filling under either of these eligibility criteria is easier, smoother, or faster?

Assuming one satisfied the continuous residence requirement as well as the physical residence requirement, N-400s based on 5 years of lawful permanent residency are easier than N-400s based on marriage processed, because one doesn't have to prove the genuineness of the marriage.

Are there any indications that filling under either of these eligibility criteria is easier, smoother, or faster?

Assuming one satisfied the continuous residence requirement as well as the physical residence requirement, N-400s based on 5 years of lawful permanent residency are easier than N-400s based on marriage processed, because one doesn't have to prove the genuineness of the marriage. The USCIS doesn't release statistics on which one is faster to process.