The latest "stable" release is 5.4.3.2. From listening to Gert's presentation the other night on Lucee 6, it looks like they may be releasing v6 in the next 24 hours or so. If I were getting ready to deploy a brand new Lucee version, I'd probably be testing on 6 at this point. However, if you're just trying to update an existing Lucee 5 app, I'd go to 5.4.3.2. If you have no issues with that, then upgrading to 5.4.4.x will probably be fine when it comes out.
That's just my take.