Both is best. The two are mutually exclusive.

Strength train, then stretch. If you're going to train conventionally, stretch before, during, and after your sets. Stretch every day. You can't go wrong with great flexibility (I'm coming from the other end - I'm quite strong, but have limited flexibility).

There's no reason why you can't do both - in fact, you'll be better off to stretch around your strength training.

Now, the fastest way to get strong is to use progessive overload... but that's a whole new ball of wax.

So do both! And enjoy bombing the ball next spring!