Errrrr....the whole table. Maybe I'm missing the point of your question. Certainly there may specifically be 1 or 2 opponents who you watch out for various reasons but there's no reason not to 'play' everyone.
Can you rephrase the question so we can understand better what you meant?
I think your asking if its smart to practice avoidance against regs and nits? Well its definitely to your adantage to play as many playable hands vs the worst players, but some hands you will be forced to play against nits and regs. Eventually if you get good enough you will have to move up in stakes and there are less fish. Its sort of a tradeoff playing against decent players at micros makes your mistakes less costly but you need to learn somewhere.
it is better to play the whole table because you are able to see more hands, and think about how much more you will win when you actually catch a hand, much more that playing 3 or 4 handed
adsthepro
the whole table so
1 there more money
2 There more people
3 There more fish to kill
4. it a nice and relax and you don't have to worry about blinds going up
5. You can learn with new people and they can coach you in a ring game