I'm type B with a little bit of type E. I'm not too picky if one of my Pokemon is 3 levels higher than the others in my party but I'll try to keep my whole team as close in level as possible. And when I'm preparing to battle a tough trainer like an Elite Four member I work until my team is at least 10 levels higher than my opponent's strongest Pokemon. I also take a long time to decided which TMs/HMs (if any) my Pokemon should learn because I always choose their movesets with the long term in mind.
In many previous games I was a Type A and would go through the games with just my starter, a random assortment of Pokemon I rarely trained, and whatever legendaries I caught.
As of now I'm Type B, though a bit relaxed on the level thing. Mainly because my team right now has a huge level gap due to late team building, leading to late training. I'm slowly closing the gap, though I've still got about 40 levels between my lowest and highest team members.
I have some tendencies of Type E as well since I'm finally seeing what a huge different the right stats and EVs make. I'm not much for competitive battling but I love seeing what kinds of strong/unusual/favorite teams I can come up with.
A little of A and a little of E. Ever since I found out about competitive battling I've kinda neglected my usual strategy. My roster is ugly and will soon be replaced with my "tournament style" roster. You might ask, "if it bothers you so much, why do it?" and my answer to that would be that I am very competitive and I want to be the best. The best I tells ya!