For an audiobook or a podcast where perfect audio quality isn't really the goal I would strongly suggest using one earbud. For listening to music where audio quality may matter more, I would strongly suggest using even one earbud instead of one travel speaker.
* Speakers are going to negatively impact people around you. There are lots and lots and lots of options like this (things for bike riding, and hiking, and all kinds of things). Things specifically designed to clip on to a backpack strap or whatever else. Lots of these are water resistant and blah blah blah.
* You can adjust the sound from the earbud to still be able to hear things around you. I promise that you can play the audio in one earbud at a lower volume with it still audible than you can play it from a speaker.
* If you only have one earbud in you're still going to have one ear unobstructed and without even low audio coming from a speaker.
* Speakers will run you through batteries faster. This isn't the end of the world and rechargeable speakers and batteries help a lot. But, it's a factor.
* You can get WAY better sound quality out of a reasonably priced set of earbuds than you can get out of a reasonably priced speaker. This may not be a factor with the types of things you intend to listen to.
What is it that a speaker will do that a single earbud will not?
* If this is a goal: a speaker will more easily let people around you listen to what you're listening to (there are earbud options for this, but generally speaking this is true)
* With a speaker you don't have to worry about shit in your ears, some people just hate that.
* Spend time to find some that are actually comfortable for you. You can spend more and get some that are actually molded to your ear if comfort is this important for you.
* Every pair I've ever seen that isn't just hard plastic (like the worst and cheapest types) come with silicone inserts of difference sizes. Don't assume that the pair that start out on the earbuds are the best size for you. Try every size. If shit is popping out when you walk or run, you have successfully found the wrong size.
* For use with an activity use a pair with a clip to attach it to your shirt/jacket/lapel. This takes the weight of the cord itself off of your ear and helps it stay in place.
* Get a pair that are designed to work with your phone or whatever. Basically all of these come with control options. You should have access to three buttons for volume up, volume down, and an action button. For modern phones the action button will pause, play, skip forward (double press), skip back (triple press), and activate the phone's voice commands (press and hold) giving you access to anything you can do by voice. In some cases a certain pair may work with android devices but not apple devices (it's rare, but it happens).
Basic Sony earbuds are fine for regular use, not great for running, do work great for walking
http://www.sony.com/electronics/in-ear- ... x110-110ap
Bose noise cancelling are really outstanding, but only if noise cancelling is something you're really looking for. Same basic design for the ones without noise canceling.
I've never found the over the ear style to be needed, but there are lots of options.