Setting aside I've tried both, we'll bore each other to death if we just assert one is better:
From first principles, Phi 2 is extremely unlikely to be better, it's a base model and doesn't know how to chat. (see README on HF repo and also "Responses by phi-2 are off, it's depressed and insults me for no reason whatsover?", https://huggingface.co/microsoft/phi-2/discussions/61)
Phi-2's license just changed and you still need to finetune it yourself. $20/month is more than reasonable for commercial use IMHO, it's a game changer.
Until I can use a truly* chat finetuned Phi-2, StableLM remains a clear winner in my experience. It can do RAG, the only other small model I've seen do that is Mistral 7B, and Phi-2 acts like PaLM acted when I would play around with it internally at Google, when it was just a base model. Impossible to use but fun toy.
* there's a couple other there, but they don't seem to have enough fine-tuning...yet
Yeah, Phi-2 is weird on chat, StableLM beats it on some metrics, Phi-2 does on others but also doesn't really have system integration yet.
The base model of StableLM 3b zephyr is actually under an even more permissive license (we didn't change in retrospect) and is the best base to train on for MacBooks with 8gb RAM, edge devices etc.
With LLM Farm quantised you can run it faster than you can read on a iPhone or whatever.
By what measure? Phi 2 seems better as far as I can tell from benchmarks and usage and has much more permissive license.