I run the Mistral-Nemo(12B) and Mistral-Small (22B) on my GPU and they are pretty code. As others have said, the GPU memory is one of the most limiting factors. 8B models are decent, 15-25B models are good and 70B+ models are excellent (solely based on my own experience). Go for q4_K models, as they will run many times faster than higher quantization with little performance degradation. They typically come in S (Small), M (Medium) and (Large) and take the largest which fits in your GPU memory. If you go below q4, you may see more severe and noticeable performance degradation.
If you need to serve only one user at the time, ollama +Webui works great. If you need multiple users at the same time, check out vLLM.
Edit: I'm simplifying it very much, but hopefully should it is simple and actionable as a starting point. I've also seen great stuff from Gemma2-27B
Edit2: added links
Edit3: a decent GPU regarding bang for buck IMO is the RTX 3060 with 12GB. It may be available on the used market for a decent price and offers a good amount of VRAM and GPU performance for the cost. I would like to propose AMD GPUs as they offer much more GPU mem for their price but they are not all as supported with ROCm and I'm not sure about the compatibility for these tools, so perhaps others can chime in.
Edit4: you can also use openwebui with vscode with the continue.dev extension such that you can have a copilot type LLM in your editor.