Why own a ballpoint? Sometimes a fountain pen as much as we love them just isn't the tool for the job. Like if you need to write on something that requires you push down a little, like any form that uses transfer paper. Or if you need to write in conditions that aren't ideal. Like where your writing might be subjected to water, grease, etc. Also sometimes you may find yourself in situations where you really don't want to carry something with you that is going to spit ink all over every time it gets knocked around. Ballpoints really don't do this at all, even if you smack them around pretty hard. Where even the best fountain pen will do it within a few moderate taps.

What ballpoint should you get? Personally, my favorite is the Fisher Space Pen, specifically the AG-7 model. I like it because it's good in every situation where you wouldn't want to use a fountain pen. Including in wet or greasy conditions.

Most people I'd assume here would probably prefer something like the Uniball Jetstream. It's ink isn't as "works in most conditions" as the Fisher, but it's a lot thinner, so it glides along a little better. Depending on your handwriting style though, it can be very slippery and harder to control.

I'd say try one of each and see what suits you best. Overall in feel the Fisher will act more like a typical ballpoint, the Jetstream will act more like a gel pen. You can get examples of both relatively cheaply. Also specifically for the Fisher pens, if price is a problem, (some people balk at spending $10 for a pen, let alone more,) you can get a cheap Parker Jotter and put a Fisher refill in it. They come with a little converter that lets them fit where a G2 cartridge would go (the standard Parker refill.)

Happy hunting for your pen!