It's easier to hook up with a flex line. And you have the added peace of mind that it's a new connection, not a reused compression end.

But if the copper looks good, I'd probably still use it.

One more thing, if you don't have a separate cutoff for the dishwasher, this is a good time to add one and replace the copper line at the same time.

I'd stay with the copper.

I think the repairman is just trying to con you into buying something you don't need.

Regardless of whether you use copper or plastic they both use the same type of compression fitting, connected to the same place on the machine and the used copper line is actually healthier than the new plastic line.

It's unanimous then -- I guess I'll stay with the copper line. The DW doesn't have a separate cutoff, so I'll check on adding that. Thanks for all of the responses!

"The DW doesn't have a separate cutoff, so I'll check on adding that."
Very simple.

Turn off water, cut line & drain, sweat in ball valve (make sure you can move the handle both on and off without hitting anything), done.

A Teflon ball seat is easier to sweat on small diameter lines (more heat tolerant).

If you sweat in a shutoff valve, make sure the valve is in the "open" position when you hit it with the heat. A closed valve could/would get damaged by the heat.

Thanks for all of your responses. I will probably hire a plumber to install the shutoff valve and water line to the dishwasher. You all do make it sound simple, but I could quickly exceed my abilities and create big problems for myself.

If you have time, check my recent post regarding using my washing machine water supply for the washer, ice maker and coffee maker. If I'm going to call a plumber, I'd like to consolidate the jobs.

I already posted a solution with an illustration...its a simple DIY