I tend to favor full AD runesets for laning now. Assuming it's draft mode, your lane opponent(s) probably have runed armor to counter you already. That's going to make your flat pen less effective (it's more effective against low-armor targets). Lots of top laners can build a ton of armor quite quickly without sacrificing much in terms of damage as well. I don't see how a few points of flat pen is going to help that much late game. Rune for your early game, it's usually going to have the biggest impact then.
I would probably only run arpen runes in lane against champions that have difficulty building armor. Also if you're surprising your opponent (like if you picked Panth and laned mid with your AP going top or something), armor pen might be a little better. AD mids versus squishy APs can usually rune for armor pen and even build some flat pen like
The Brutalizer. AP carries generally have a tough time counter-building so early in the game without throwing all their damage out the window.
Full AD is superior for bot lane imo considering the amount of armor buffs down there and the fact that almost every bot laner will have armor seals. Supports often take armor marks as well.
I would probably only run arpen runes in lane against champions that have difficulty building armor. Also if you're surprising your opponent (like if you picked Panth and laned mid with your AP going top or something), armor pen might be a little better. AD mids versus squishy APs can usually rune for armor pen and even build some flat pen like

Full AD is superior for bot lane imo considering the amount of armor buffs down there and the fact that almost every bot laner will have armor seals. Supports often take armor marks as well.

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Armor Penetration is better
If your having trouble last hitting than you need to practice more
Not neccesarily if you play someone whose every skill scales with ad. You start lvl 1 with +15 or so, you get HUGE damage and on each aa between skilling like Riven should do... that is burst lvl 1 if going broken wings.