I think that's Prince is better then Dark Prince. First off, the Prince has more health then the Dark Prince even with the Dark Princes shield. I don't really see how much of a difference the Dark Princes shield makes because when they are added together (lvl 8 vs lvl 8) there isn't as many hit points as the Prince has. And even though the Dark Prince does have splash damage it doesn't even make that much of a difference. The Prince does more damage then the Dark Prince (could be because of splash damage). And to me it just seems as if the Dark Princes charge is slower then the Princes (opinion). And Prince you can get early so you have more time to level it up but the Dark Prince you have to get alway the way to Arena 7 (2000+ trophies) and it's pretty rare to have in him in the shop or get him from a chest.
Dark princes are so much better. Though I have not used them they are very powerful. They can't simply be taken out by a skeleton army. Princes in the other hand are crushed by them. Even if the enemy puts minion horde you can arrow. To do a lot of damage you must put both prince and dark prince. You could use mirror mirror dealing twice the damage.
You said that Prince can be countered with skeleton army but couldn't you just arrow them (like minion horde)?? And you can't go off of the assumption that Dark Princes are better just because you see them in replays, it really depends how the Prince and Dark Prince are used. You won't nessicarily do more damage with double Dark Prince because they can easily get distracted.