ALM 12.20 has patches available to address several known issues and tHP is constantly developing patches to be released in the future got address other issues that may still exist. We have found that with the patches in place ALM 12.20 is very stable and complete (some of the patches have changed the versioning listed on 12.20 to 12.21, the same as 12.53 is a patch/enhancement that changes the version number from 12.50 to 12.53).
I wouldn't say that it has ''lots of issues'' or any more issues than other versions initial releases contained within them. Is there something specific or a certain issue that you are trying to avoid, as sometimes upgrading would also bring about those same issues along with others that exist. The only thing that I know at this point that would keep a recommendation of upgrading to ALM 12.53 from occurring would be the need for third party add-in support, such as UFT (as of now that would require the upgrading of the software to at least the 12.53 version of that software to maintain functionality with the AKLM system, and there may be other issues with syncing softwares being used as well since 12.53 is so new).
Hope this helps.