well here is something I can speak about from personal experience. I've owned my two boas for the last four years. Great animals, very tame, easy to care for IMO. Great to handle, easy to predict, feeding is simple and straightfoward. I can feed them, leave for a few days and come back with no worries, so long as power is maintained and water is there. I've always had a fascination with large snakes and they are the perfect large constrictor pet. They are, however, not spectacular animals to watch. They hide in their logs, most activity is nocturnal, and their speed is only truly realized at feeding time.
Monitors are on a whole different level. I recently bought a black roughneck (very similar to a dumerils) and he is GREAT. However, feeding is more involved and not as well documented, IMO. Housing is more involved, basically generally husbandry is much more intricate and time-consuming. All that being said, I LOVE MONITORS. The interaction you have with them, their curiousity and active nature, all make them incredible animals.
Basically, it boils down to this. If you want an animal to put in a cage, feed occasionally, look at and take out whenever, and just keep warm, the snake is for you. If you are looking for a more involved pet that will reward you with interaction and curiousity but take more of your time and effort for its care, than the monitor may be for you. Dont get me wrong, I still enjoy my snakes and all that they are but monitors are a completely different kind of pet. Did I miss anything?
OH YEA, PLEASE PLEASE DO YOUR RESEARCH FIRST. Do not go buy a monitor or snake on a whim and then find out about it after you have it at home. See what the requirements for each are. Find out how big it will get, how much space it will need, what to feed it, how warm to keep it day AND night, and any other special considerations. I hate to see SO many monitors and large snakes alike for sale because the owner bought it when it looked 'cute' at the pet store, not realizing that nice 12" nile monitor is going to grow up to be a 6' long tangle of tail and claw that may or may not be friendly.
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Chris
1.0.0 Columbian Boa
1.0.0 Columbian x Hogg Island Boa
0.1.0 Argentine Rainbow Boa
2.0.0 Bearded Dragons
0.0.1 Black Throat Monitor
0.1.0 Black Rough-neck monitor