At your height and build, you'd probably be comfortable in all three. But because your DS is on the tall side, you may find that the Ergo may not be tall enough in the back as he gets bigger. It's one of the shortest back heights of all SSCs.
The Beco has two models now, the Butterfly and the Gemini. The Butterfly might be a good choice if you think you may want/need an internal harness for learning bck carries. Honestly though, I found it kind of a pain to use with older kids. The Gemini has more height to the back then the Butterfly when the head supprt is pulled up, so it may fit an older, taller baby a little better and does not have the internal harness. You would also be able to cross the straps in an "X" while doing a front carry (can't do with a Butterfly).
The Boba is a nice carrier for older babies and toddlers. It has a pretty high back but some people complain it's a bit to narrow in the seat for older toddlers. They do have the foot rests to help with that, though I have yet to meet an older toddler willing to use them!
Another option would be a BabyHawk Oh Snap. It is both tall and has a nice wide seat. For what it's worth, a lot of people say that they really dont even start to fit well until about 1yr old, because it really is a bigger carrier meant for toddlers. It sounds like your DS is pretty big though, so he might fit. It also gives the option to cross the straps in the back too.
Hope that helps and I hope you find the perfect carrier soon!
*mama to c 2/2000, v 2/2004, p 9/2006, and h 12/2012*
one of the mamas behind BeanTreeBaby.com ...Gear for Growing Families!