Stock configuration; 2.4 GHz Core 2 Duo, 4 GB RAM, 250 GB HDD. I had stuck with Snow Leopard for a long time, then was on Mountain Lion for a while until I recently went to High Sierra. Wow, just wow. What a terribly slow and buggy operating system! Not at all what I expect from Apple; if the hardware isn't able to run it, I would expected them to drop support for it by now. But, based on reviews and other posts I've seen about High Sierra, it just seems to be a bad egg. Maybe it will be improved with patches. Anyway, I was wondering which version of OS X/macOS would be best to run on this MacBook Pro? It has been a very trustworthy notebook over the years, though I put it away for almost two years before recently breaking it back out. I downsized my computer collection, previously I had been using a 2011 Core i5 iMac with original Sierra, but decided four computers was too many on the desktop. Apologies if this is a recurring thread, I did a quick search and didn't find what I was looking for here but I may just not be familiar with this forum's search functions. I'm hoping that I will be able to upgrade to one of the newer MBP's soon (no vanilla USB ports? crazy town!) but have tasks to get done that require a clean and efficient operating system until then. I appreciate the input.