If you just need a loop, use a Butterfly Loop.  But if the task isn’t critical, and you need to thread the loop around or through something before closing the loop, you can use the bowline.  If the job needs a truly secure end loop, try the Water Bowline if you can't use a Butterfly Loop and a hitch isn't appropriate.

The Bowline isn’t generally bad, but it isn’t secure enough for critical applications, especially where the line will see a lot of jerking and/or where stiff or slippery rope is used.  If you tie a Bowline in polypropylene rope, and give it a few jerks, you’ll quickly discover its lack of security.

If you're going to use it, please don't tie it the landlubber's way! Learn to form the signature Bowline half hitch part by twisting the end of the line over, under and upward around the standing part, in one quick motion. You’ll need to know this before moving on to the Water Bowline. Not only is this a quicker method, it also greatly reduces the odds of you tying the knot incorrectly.

RUNNING LOOPS

Like any loop, the bowline can be made into what is known as a running loop shown below, which causes the loop to act as the sliding part of a noose.  This can be done in three different ways.  You can tie the loop around the standing part of the rope, or you can run the other end of the rope through the loop and pull until you get the running loop down to size, or lastly, you can pull a bight of rope from the standing part of the rope through the loop, and then carefully work the torsion out of the original loop.