Unless Construct 3 has some real bugs that will prevent you from making the game you want, go for Construct 3. That is where future of Construct lies.
But, right now it does not help you make better games, that is why I'm still on Construct 2. No need to switch to 3. ( hey, like I've said before, make my life easier by adding a working adsense or adsense for games plugin and you have my $99, by the way an experienced javascripter could code that in 2 days, so really what's the holdup? )
Trying those free versions is always a good idea, but considering their limitations I doubt you will be able to tell the difference ( other than the general feel of each ) . You can't really find major bugs until you have a fairly large project and start exporting things.