well, i own a water dragon and my roommate owns 4 igs...
i can definitely say from experience that water dragons are your best bet. water dragons are a lot more tame. 3 of the 4 igs that she has are mean. she treats them well and has been trying to tame them, it just aint happening (she bought special handling kevlar gloves... her largest one bit so hard through one glove, that injuries of the hand still resulted).
ig upkeep is definitely more of a hassle (water containers have to be changed several times a day). judging by food costs too, water dragons are cheaper to keep up with. b/c ig diets are entirely greens and fruits, the wide variety of greens and fruits have to be fresh and fed daily, sometimes more than once daily in order to keep them real healthy.
however, there is a slight bonus to the vegetarian diet, my roommate doesnt have to deal with crickets, mealworms & superworms. i know my expenditures on insects comes to much less than my roommates' on fruits and vegetables. but, i deal with noisy crickets, some escaped crickets and i have to feed the crickets & worms too (it is still cheaper than having igs though).
the initial investment in the right materials for your lizard's happiness should be your biggest concern. the initial costs will most likely be your biggest.
some tips that make having a water dragon a lot easier... buying a humidifier for human-use, running a tube into the dragon's cage, then putting it on automatic timer. also, buying a fluval water filter, for his water tub, helps keep the water cleaner longer.. altho, i still change it every other day. i also keep my lights for him on timer too. that's really helpful in the mornings.
well, good luck.