I'd agree with those recs. I'd suggest 4 and 5 equally.
I don't think 8 is a terrible game and I fail to see how any DQ fan could see it that way, but it does have some pretty heavy flaws that go against what DQ had built almost 20 years up towards being, fast combat being one of them. But the characters, scale of adventure, quests, touch my little heart. I'd love a remake of 8 on 3ds, and by extension 7, as well.
You'll notice I put = signs on my list. That's because ranking one DQ over the other is a fool's game. I find them each - for the most part- equal in quality, but with a different set of strengths, weaknesses, and focus. I think it's about the only long running jrpg series or series period, I can say that about. DQ is damn consistent with me.