I would highly recommend gemini 2.5 pro too for their speech quality. It's priced lower and the quality is top notch on their API. I made an implementation here in case you're interested https://www.github.com/akdeb/ElatoAI but its on hardware so maybe not totally relevant
I'm using LiveKit, and I indeed have tested Gemini, but it appears to be broken or at least incompatible with OpenAI. Not sure if this is a Livekit issue or a Gemini issue. Anyway I decided to go back to just using LLM, SST and TTS as separate nodes, but I've also been looking into Deepgram Voice Agent API, but LiveKit doesn't support it (yet?).