I tried ChatGPT, Perplexity and Gemini extensively along Kagi Assistant.
I like Perplexity for its various models. But it's crowded with features like newsfeeds. It has Spaces that work really well to create custom projects with attached files and links, but I found links are not to be trusted. I don't see when Perplexity is really going to a link and indexing into the context and several times it had no clue there was something attached. So weird bugs there.
Furthermore, I hate the layout. Chats just get listed with the FULL question in the sidebar and it makes it so hard to find conversations if you don't diligently rename them. And within the chat, Perplexitys layout makes it super hard distinguishing where my questions are and what the answers were. In a long discussion you're playing a game of hide and seek. Perplexity has an annoying voice mode on mobile that is basically useless to me to hold any discussions.
ChatGPT has a great layout, great projects, a great chat mode. It's one of the best apps of them all that I used. Super clear in its design. Only downside is: You can only use ChatGPT, which is notoriously happy and thinks every crap I produce is the best in the world. Golden! What an idea!
I really like Kagi and I come back to Kagi Assistant often to use other AIs. It's fast, it's clean, it's strength is in its simplicity. I like you always see what AI gave the answer. An info you have to click to see in Perplexity. The answers are plain in the design, which makes it easy to read. I'd like a better visual different between what I input and the AI responded. ChatGPT has a great chat interface for that. As if I'm typing in WhatsApp. Easy to see what was written by me.
Features I miss in Kagi: ImageGen (apparently being worked on). I'd like Audio Transcriptions from audio files. I'd like a better voice input mode so I don't have to type long instructions into the input field - the voice mode is useless sadly. if I only pause for half a second to think what to say, the assistant stops listening. no conversation or longer dictation possible. Super annoying.
I'm sure at some point I'll switch to it full time.