Late to the party here, but I vote Boa.

Much easier to handle when at size and that size is usually a little smaller than even a dwarf retic.

How big is your little BCI now? Have you held a large/adult female BCI or BCC? Have you handled a retic?

I know you had a lot of questions early on about your little BCI and, in my opinion, BCI's are much easier to house, keep healthy, and handle. You were also looking at upgrading to a better enclosure, but that takes time, funds, and space. Did you solve those issues and have room for another large tank?

I've been keeping snakes/reptiles for the better part of my life and just recently, at 37 (now 38), got my first BCI. I have the time, space, finances, and skill level where I feel I can easily provide for Behira (my BCI). It wasn't until two weeks ago at the NH reptile expo that I held and adult female BCI (7FT and 16 pounds). I was shocked how easy a full grown BCI was to control and handle. However, I had been worried up to them how Behira might be at 20 pounds versus 2 pounds that she is now. Seems like she will just be a gentle giant like the girl I held at the show.

I am not telling you what to do, but I am encouraging you, as I get the sense that you are relatively new to the game, to take your time and make wise and informed decisions. Many experienced snake keepers never get a retic, dwarf or otherwise, and in many states it's illegal anyway (mine - CT). They are a handful, even compared to an adult Boa.

Also, keep in mind that a healthy Boa that's fed properly will live 20-30 years. Not sure about retics, but I believe they are long-term commitments too.

Make sure you are making a decision and that you can care for the animal (animals) for their lifetime.

I want the best for you and your current and soon to be growing collection. Sorry if I sound preachy, but I've had to learn my limitations (in my case health issues and time that I can spend with the animals I have limits me to what I have now), and as difficult as it can be when what you want doesn't align with what you are able to do, it's best for everyone to be realistic.

I hope I am misreading the situation and please forgive me if I am, but please do what's best for all involved; both you and the growing reptile collection.

In any event, if you are getting another snake, I vote Boa all the way, and suggest a cool BCI morph, or as you are looking for, a beautiful locale BCC (keeping in mind that they need to be grown slower, are a little more sensitive to environment than BCI's, and that ultimately, they get bigger).

Good luck and keep us in the loop.