There are actually a lot of differences between those carriers, but they are all soft structured carrier (aka buckle carriers) so they all have similar qualities. I know it can be frustrating to sort through all the kinds of carriers out there! If you are really lucky, you may be able to find a babywearing group near you where you can go and try different carriers. Otherwise, you just have to read, read, read and see what people say about each kind. I'll try to help a bit with the few you mentioned.
The Action Baby Carrier (ABC) is a great carrier at a great value. They are simple well made carriers, but don't have some of the bells and whistles that more expensive carriers have. Their padding isn't as thick as on some carriers which is a plus to some people depending on your personal preference.
The biggest difference with the Beco is that is comes with an infant insert and an internal harness that allows you to securely put baby in before putting the carrier on. Some people really like this since it can make doing a back carrier easier for them, although some people don't like the harness at all. Again, it comes down to personal preference.
The Oh Snap is designed with a longer body which makes it too big to use with most babies under 6 months and even some older babies that are on the smaller size. This carrier is targeted more towards older babies and toddlers. It is a really great toddler carrier and you can easily and comfortable use one with a child 2+ years old. That being said, it is also one of the bulkier carriers available and the padding is really thick, which makes it more comfortable, but also more bulky/heavy.
Probably the best place to start is trying to decide what your needs are. Do you have a newborn or an older baby? Is your baby big or petite? Do you plan to use this carrier through toddlerhood or will you get another one down the road? Also, you want to consider your size. Some carriers have a better fit for one body type or the other. So if you are petite or extra fluffy, there are different carriers that may work best for you.
Sorry if I am just making it more complicated!!! Just ask lots of questions. People are happy to tell you what worked well for them and can recommend brands that may also be good for you! Good luck!!!
I just bought about 5yds of no-fray fabric & cut it in half vertically & viola! 2 wraps for total $10.
I guess maybe I should post a thread about all of my particulars and see if there's a few mamas out there that are in the same boat as me. 
I used this "pattern" as well, and LOVED my no-sew wraps with DD. I'm doing the same thing with the next little one. Amazing how so little money and such simplicity can yield one of the most used and loved baby items ever! OP, here's the "
