I like https://nostrudel.ninja/ because it supports most nostr features.

The speed is based on the relays that you use. I know this because I had terrible issues with android apps and speed. Using about 5 to 10 relays seems to be ideal.

There's always a delay when launching any client because it's connecting to all of them.

For a native desktop client, I like Nostrmo. https://github.com/haorendashu/nostrmo