Romantic lullaby is better slightly, but not enough so to warrant taking it solely for that reason. Romantic is a good overall repertoire to pick, and will do good for a first time bard, but can be good for vets to.

Grand noturne is superior with tragic. Romantics generally won't kill people you just land an initial fiend on, except maybe a cloud, where as tragic might. The differences are pretty noticeable, which is why people play tragic.

Nocturne of fright is about the same as grand nocturne in terms of the potency between the reps.

I played a decent tragic bard (half-elf) in the chasm, and had a decent elf romantic bard in the village when the purge hit. I didn't find much to be really altogether different and you can play them both very effectively. Bards are a bit more dependent on your race/cabal choices than the repertoire in terms of how effective they end up being. I.e. a battle bard might want to be more defensive so be a higher dex class with maybe romantic for better healing to make up for lack of available preps, where as others can be more offensive and compensate with Dam reduction.

Preferred rep does impact available edges to a very small degree, as there are edges based on it. i.e. serenade (romantic) killing joke (comedic) and there is one for epic. No edges exist for tragic preferred.

People have played more bards than me that probably have more experience, but depending on if you want to try to seal with fiend or other tactics is largely the reason for taking romantic or tragic. The other two also have their perks.