5
Mmmm... I understand why people get confused when they hear something like this
PHP 4.4.3 has been released after PHP 5.1.4, does that mean I was supposed to "update" my 5.1 to 4.4.3 ?
If you're using 2.2.3, you can update to 2.2.4.
If I got it right: 2.0.x and 2.2.x have many differences, and as 2.2 doesn't meet the developers' quality standards, the 2.0 code is going to be favored in the future. Now, if 2.2.3 works for you: keep using this branch, update to 2.2.4 if you can, and to 2.2.5 later if there's one.
There has been a "downgrade script" to switch from 2.2 to 2.0, but it is only for people who really need it and know what they're doing. If that's not your case: stay out of troubles, and update to any 2.2.x you may see, the fact developers choose to reuse one codebase or another one is their business, and doesn't concern regular users (you will be able to upgrade to 2.4 later, whether you're using 2.0, 2.2 )