No treatment, including imiquimod (Aldara), is more than about 60-70% effective.
In theory,
Aldara might be better at preventing recurrent warts, but
in the real world there is no obvious difference in cure rate or recurrence rate between Aldara and any other treatment. If one method isn't working well, trying another makes sense. Aside from podophyllin and Aldara, other options are freezing, repeated laser- or electrocautery, and trichloroacetic acid.