The only reason to start with FE8 is it's the easiest in the series
But FE7 isn't too bad difficultywise on normal mode and is the only one with a forced tutorial so if you're going that route there's no reason to pick FE8. Also FE7 is a much better game.
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I tried to have a fierce rivalry with SuperNiceDog, but he made me look worse than a GameFAQs Contest!