Without taking a deeper look: All Basic dialects are very similar (like VB.net and B4J). So it's not worth to compare the syntaxes (will be >95% the same).
Better: All B4x versions are compatible so you can reuse the code with some minor changes. Example: B4A-App. Except of handling views you can take your subs and use it in B4J and vice versa. This is the biggest plus. All libs basic libs are compatible.
And... B4J is for free!