Is Titan Better or Mars? Isn't Titan better to colonize than Mars? It has a thick atmosphere which is made up of nitrogen like our planet's. It doesn't have a magnetic field, but it does get a type of protection from Saturn. Maybe the only downside I see is that it is too far away. While Mars has neither a thick atmosphere nor a magnetic field, it is bombarded with solar radiation every day.
We have no practical means to travel to either planet and set up even a base, let alone a colony.  As such neither is better.

Also note that we have no reason to do it and we would need an extremely good reason because it would almost certainly involved the expenditure of vast resources to even set up a base, let alone a viable colony.

In a practical sense neither have any real human habitability options other that entirely sealed bases.

However current knowledge suggests that the geology on Titan would be really challenging.  We'd be operating a base at significantly higher temperatures than the local norms and as such we'd always be subject to problems in a atmosphere with active weather.  The only attraction on Titan is studying the locale, but we'd have done that in enormous depth before we could even consider a colony, so it's a mute point.

Mars is closer, less hostile and more familiar.  We'd go there before Titan for the simple reasons it's easier, cheaper and more likely to succeed.  But again, why ?

But we'd be unlikely to do either before we'd establish a viable self-sustaining Moon base of at least "colony" status.  Again that's not even remotely possible and would not be possible without a unified global effort.  Well this particular globe can't even agree the wording of one sentence in a document about it's own report on climate change.  They can't even agree about one lousy word !  So no one is going to even start talking about the possibility of setting up a committee to discuss the likelihood of setting  up another committee to start planing for a colonization effort research program.

In short, even if we solved the technical problems to make it worth deciding which place to colonize, we have no political chance in Hell of actually doing it.  Humanity will die squabbling in a committee room.  No colonists required until we replace humans with something that works.  Skynet anyone ? :-)