Honestly I didn't use to think that it was a smart idea to separate the field into sectors because correlations used to be a lot higher, but now I think it's not the worst idea:

1. Legacy coins
2. Privacy coins
3. Non-blockchain coins
4. As sad as it is, below $1 coins (I really don't want to admit this is a thing, but it is really seeming like it)
5. Fast, low fee (or zero fee) coins

So on, so forth. It does seem that they pump in groups now far more often than they did before so may not be worst idea in world to diversify into groups as opposed to past where I'd say just pick whatever altcoins you like best even if that makes you concentrated in only 1 or 2 "sectors."