I use a Cateye Strada Cadence. I got my first one about 7 years ago. I would sometimes loosen it from its holder while wheeling my bike around (so as not to mess with my stats - as it'd no longer make electrical contact with the sensors) - and one day I forgot to click it back in all the way when I got back on my bike. I hit a bump and it popped off and then instantly got run over by at least one car. That busted it. I called up Cateye asking if they'd sell me just the computer and they just sent me one for free. To be clear - this was 100% my fault. I still use the replacement one they sent me. Quality product with awesome service.

Of course, if you don't need cadence, I'd suggest a slightly cheaper Cateye model. But I think cadence is super useful (and something a smartphone will have trouble offering you!)