The NEC does not make distinctions between stranded and solid for overcurrent protection ratings. Stranded does cost more and does not conduct quite as well as solid where a choice is available. For those reasons, my choice is solid unless there is some offsetting reason to use stranded. Tell us more about your application.

I recently purchased by estate a concrete block cottage built in 1950 and I'm renovating to rent in the future. I noticed the oven protected by double pole 40A breaker has stranded wire and there are 2 double 30's in the service panel with stranded wire that I cannot tie to anything. There's no central air and the HW heater is accounted for. The structure is only 800 sf. There are other issues with the electrical such as the 10-3 for the HW heater which is spliced and taped with masking tape and a switch feed terminated in the attic with wire nuts.

I need to do some more investigating, but thinking of rewiring everything and I wanted to know if I can run no. 8 stranded to the oven outlet. Thinking the stranded would be easier to work with.

So the existing stranded is "free". That is the best price possible. But present code requires a separate equipment grounding conductor, which probably is not existing.

"But present code requires a separate equipment grounding conductor, which probably is not existing."

3-wire services for ranges and dryers are grandfathered as long as no changes are made to the circuit.

The AHJ gets to decide what they consider a 'change' that would require running a 4-wire service.

Stranded is used once the gauge exceeds a certain size, because it is easier to make and use. I don't recall what that size is, but I figure it is around 10 or 8.

Brickeyee, what constitutes a change? I'm going to research the model no. but I would guess it's from the 60's and it still works. It has 3 eyes, push button controls and an integrated receptacle possibly for plugging in a coffee pot. I anticipate replacing the cable so will I have to use a 4wire service? If so, how will a 4 wire cord attach to the range because I'm sure there's only 3 termi?

Brickeyee, what constitutes a change? I'm going to research the model no. but I would guess it's from the 60's and it still works. It has 3 eyes, push button controls and an integrated receptacle possibly for plugging in a coffee pot. I anticipate replacing the cable so will I have to use a 4wire service? If so, how will a 4 wire cord attach to the range because I'm sure there's only 3 termi?

"If so, how will a 4 wire cord attach to the range because I'm sure there's only 3 termi?"

The bond between neutral and the chassis ground is removed when a 4-wire cord is installed.

The 3-wire cord simply bonds the chassis ground to the neutral and uses the same wire for both.

It is up to the AHJ to decide exactly what constitutes an 'alteration' to the circuit.

Some are harder nosed than others, and will not even allow repairs to the circuit.
New receptacle for ANY reason, new branch circuit.

Others allow minor changes like moving the receptacle a few inches for a new stove (there is no 'standard' location for a receptacle for a range), or replacing the receptacle with a like type, as long as the wiring is not extended.