“The internet connection is choppy.” Does this sound natural to mean the connection keeps going on and off? What informal words would people use? Thanks.

Yeah, it sounds fine. I might say "unstable" or "spotty" myself. 

Technically the answer is "unstable" but many would call it "glitchy" or just variants of poor/bad. Choppy usually refers to sound and bodies of water.

You can say its cutting out, or breaking up too

"Choppy" makes me think of water. Boats deal with "choppy" water a lot, or airplanes have choppy air. I'd say "The internet connection is spotty" or "finicky" or just "weak" or "bad".

Choppy is an interesting choice. It does sound natural but that doesn’t mean it’s right. “Choppy” as term used in English when referring to radio signals or technological connections. It’s pretty self explanatory, meaning the connection or signal literally “sounds like chopping”. It is really easy to hear when a radio signal is being choppy and by extension “choppy” can, and was for a longtime, used to describe telephone and even TV signals. However, considering that internet connections do not have an auditory component is it really appropriate to describe them as “choppy”? Arguably, yes if only because, like so much about tech, the descriptive terms used in English often reference antiquated and obsolete predecessor tech. We still “hang up” the phone despite not physically hanging the receiver from anything. So yeah, I would understand “choppy” in this instance to refer to an inconsistent signal or connection. If you wanted a safer word, I would go with “spotty”, “weak”, “poor” or just “bad”. Having a “bad connection” is probably the most common way to express it, without potentially sounding like a WWII radio operator. TLDR; despite that “choppy” literally means to have the auditory quality of chopping, the terms around tech don’t need to be literal between mediums.

Yes! Choppy sounds perfectly natural and works well. Personally though I would just say "keep cutting out" as a verb phrase.

Yeah that works... we would certainly know what you meant, but we say things like "the internet has been up and down" , "The internet has been intermittent." etc..

"Flaky" works well too to say it's been unreliable.

I would understand the meaning if I heard it described as "choppy," and it's not an outlandish term, but it's not a common way of describing it. Spotty, hit or miss, unreliable, erratic, or unstable would probably all be better terms for it.

internet connection is sporadic, but that implies more of a chronic issue

The statement is excellent. I've never heard it before, but I knew what you meant right away.

I might say 'sketchy' or 'flaky' or 'iffy'. Or just 'bad'.

Despite what many people here have already said, I would never use the word choppy. "The Internet connection... is spotty/goes in and out/ is hit or miss" would be the top three informal options I would use.

You would def be understood even though spotty or flaky is more common.

Yeah that's a pretty common way to phrase that.  There are other ways to say it, but this is definitely a way a lot of people would say it. 

You would be totally understood if you said that! There isn't a correct answer here, but as others have said, spotty is probably the most common adjective to describe bad internet that's similar in tone to choppy.

Perfect. If someone told me any signal was choppy I would understand immediately.

"Choppy" sounds more like inconsistent performance. It's fast one moment, slow the next. "Intermittent" means it keeps going on and off. If that feels too formal, I guess you could say something like, "The internet keeps going out" or something like that, but "intermittent" really is clearer.

Crappy internet

Yes - where I live we use the word laggy or lagging but I would understand what you meant by choppy.

Chop or choppy usually refers to air or sea turbulence. Choppy seas or pilots will sometimes refer to air turbulence as chop. For an Internet connection there are many words you can use which are better suited: 1. Unstable connection 2. Laggy (more informal) 3. High latency (very technical term) 4. Intermittent connection 5. Unpredictable connection 6. Buffering (video connections)