You really can't beat a regular Columbian Boa constrictor, if this is you first venture into Boas, I would suggest getting a common BCI, or Common Boa Contrictor. They are very easy to keep, pretty low initail cost, and most remain very mellow. They where the first boa I every had. When you get into the BCC or "True Red Tails" which I think is what your talking about, when you say Amazon red tail, you have to be carefull cause some of the cheaper ones are wild caught and most of the time are very difficult to get feeding and most are pretty fiesty. For your first boa, would really go with a common boa, and go from there, most of the time you can find really healthy ones for under $100, where as most other locales are twice that or more for initail purchase cost. But be careful, they are addictive and soon you will want to purchase more...LOL Good luck and keep us posted on what you decied. There are also Central american locales which generally stay smaller in size, and also the island boas, such as Hog Islands. They are all very interesting and can be very different from each other, but as beautiful and aluring the BCC's or "True Red Tails" can be I would wait till you had some experience keeping boas before venturing into the larger Boas....I have kept Boas for 15 years, and have only had 1 BCC ever in my life...but on the other hand have kept 100 BCI's over the years. The BCC I got was wild caught and I had so many problems it made it extremely depressing to keep. Someday I might get myself one, they are beautiful. SOrry for the long rant...Good luck.
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"Life is a Safari"