I've not been happy with either, but if I had to do it, I'd just use a lower native ppi.
I did a print for a friend from a low scan of a 35mm neg and the ppi was really low for 13"x19" - IIRC around 80 ppi - possibly even less? I upscaled it (can't remember what to) and it was "not bad" - my exact words I think.
I recently did an A4 print at 90ppi from a pretty poor low quality jpeg and described that as "ok".
(For both of these, they were fine at distance. Close scrutiny though is what where talking about here)
So for me - it's a choice between "not bad" and "ok". However. My eyes aren't that great. I can print at 200ppi and still see a fab print under close scrutiny. In fact, with 20-20 vision, the eye can resolve around 800ppi at 4" which is the closest focussing distance for your un-aided eyes. 300ppi comes from magazine reading distance (12") hence it's often used by print publishers.
So taking into account my eyesight, and personal taste, I'd choose lower ppi over upscaling. I find upscaling tries to sharpen the image and adds artifacts that I really don't like. Up close, it looks like a badly sharpened image vs a low ppi version which looks blurred up close. Also. Upscaling is adding stuff to the image, which I just 'don't like' the idea of. It's also another software step and I don't really enjoy PP work.
Ultimately, it's going to be down to personal preference. It's easy to replicate. 2 prints. 1 upscaled, the other native ppi. Both the same size. Actually - that sounds like quite a good experiment for a blog post... But at the end of the day - it's your preference that matters.