It depends on what your idea of "difficulty" is? I would consider very aggressive fish that fight all the time and make a mess when they eat as "difficult," as well as primarily wild stock that may not take to pellet foods. Geos are pretty calm for the most part in my experience, and accept most foods. The pikes in the hobby are usually wild caught and a bit more aggressive, so that can be a bit of a challenge to get them to accept pellets.
The larger bodied cichlids like the pscittacus and vieja can also be aggresive but my main concern living with those more aggressive cichlids would be the Geos, and the altifrons and several other types of geos grow large enough to not become lunch for your big boys. And don't think that just because the geos are pretty and relatively calm that they cannot hold their own. They have strength in numbers.