I'll get straight to the point and I won’t ramble on about this. It’s a pretty straightforward question. What do you prefer in a league title, or in group stages, or just in general, when the points are tied: goal difference or head-to-head?
In La Liga, when both teams are tied at the top of the league with the same amount of points at the end of the season, they look at the head-to-head matches to decide the winner. In the Premier League, when both teams are tied with the same points, they look at the goal difference, and the team with the superior goal difference wins.
Personally I prefer the goal difference for 2 reasons.
Firstly, let’s take a hypothetical example in the Premier League. Let’s say that Arsenal and Manchester United were challenging for the league title this season and that they were level on points on the final day of the season. During the season, United had beaten Arsenal 8-2 at home and, again, hypothetically, Arsenal beat United 2-0 at their ground (I know that didn’t happen, I’m asking you to just imagine the scenario). Do you think it would be fair that Arsenal’s fate will then be decided by their 8-2 loss to United? Arsenal might have been 18th at the time of their 8-2 loss but are in top spot at the end of the season level on points with United. It’s a bit unfair because normally title challengers change throughout a season. A team might be in the top 2 positions until December and then fade away, and vice versa, a team might be struggling until Christmas and then suddenly bounce back.
Secondly, when it depends on goal difference with the teams level on points (and sometimes goals), it means both teams have to go for goals, making it more entertaining. Refer back to the final day of the 2009-2010 Premier League season when both Chelsea and Manchester United had to beat their opponents by high margins, in case either one of the teams slipped up (despite Chelsea having a 1 point advantage). That didn’t happen, but both teams attacked in full force resulting in an 8-0 win for Chelsea vs Wigan and a 4-0 win for United vs Stoke - making it a simple case of outscoring the opponents by the highest margin.
That's my personal preference, but it's a question that will differ between all of your answers and is pretty subjective. So what do you prefer: goal difference or head-to-head?