Regarding context windows, Gemini currently offers 1M tokens (reportedly increasing to 2M soon), GPT-4.1 also handles a large window of 1m tokens, and Claude provides 200k. In my experience testing them with large code files (around 3-4k lines), I found Gemini 2.5 Pro and Claude 3.7 Sonnet performed quite similarly, both handling the large context well and providing good solutions.
However, my impression was that GPT-4.1 didn't perform quite as well, While GPT-4.1 is certainly capable, I feel Gemini has a slight edge in this area right now. Based on this, I'd lean towards using Gemini 2.5 Pro for extremely large contexts needing high-quality results, GPT-4.1 for backend logic, and found Claude 3.7 particularly effective for UI interface tasks.