Other physical distinctios are:
1. loreal scales, the scales between the nostril and eye. In Columbians there will be 2 scales, in Argentines 3.
2. Argentines have more of a defined pattern going down the back from neck to top of the tail. These are just 2 white stripes on the each far side of the back.
3. Argentines come from cooler areas (generally) and can be more tolerant of cooler temps.
This is all stuff you can read at the Agama International website. It is full of info on this type of thing and provides pictures of examples that you should take a look at rather than try to decipher my descriptions. It'll also tell you just about anything you ever wanted to know about Argentines.
As far as attitude, all I can tell you about is my Columbian. She's about a year old and is an eating machine. Not a biter but still doesn't like to be handled. I fully anticipate getting scratched to heck and back with a side of tail whipping when I remove her from the cage. All Columbians aren't the cujos you may read about here, but I'd still say mine is the exception to the rule as far as not biting. That's also not to say there aren't some nasty merinae out there. If you're choosing, I'd go for the Argentine. Still wouldn't trade my girl for nuthin', though.