Pros - Watching/caring for them growing from juvenile (if under 10cm) to adulthood.
Can't really think of a con when it comes to juveniles. We had more problems with the adults we bought (ie 5 raised on gravel and constantly pooing out gravel/pebbles; 3 of which were raised in poor water quality conditions therefore had damaged or nonexistent gills and were extremely stressed and took a while before they regenerated and settled down).
We tended to watch ours all the time! They do get fed more often (twice a day till they're about 12cm, then once a day till they're 15cm in length) than an adult.
When you buy adults the chances are you may be buying a sick one or one that comes with problems (ie. it may have been cared for improperly by petshop or previous owner). Never ever buy one that's overly skinny, floating, missing limbs or gill filaments (the fluffy bits on gill stubs) or that might have patches of mucus, peeling skin or that you think might need rescuing because of its appearance. You'll basically be giving yourself more work and stress trying to care for it.
When you do buy your axolotls, try and buy from the same source at the same time. And put one into the tank and keep an eye on the water parameters, keep the other one separate for about a week and then add it - this is so the tank copes with the bioload of the axolotl/s being added.
If they come from different sources at different times ensure they're kept separate for minimum 30 days to ensure both aren't sick and won't pass anything onto the other.
