Being at a resort with a poor internet connection has made the performance differences between Nostr clients strikingly obvious. nosotros seems to be the best. Of course, this might require a deduction based on how well it adheres to the Outbox model, so a simple comparison based on initial loading speed alone might not be a fair assessment.
Originally, the top performer in this area was nostr:nprofile1qqs24yz8xftq8kkdf7q5yzf4v7tn2ek78v0zp2y427mj3sa7f34ggjcpzamhxue69uhhv6t5daezumn0wd68yvfwvdhk6tcpzpmhxue69uhkummnw3ezumt0d5hszrnhwden5te0dehhxtnvdakz769wywf but it slowed down a bit after the Outbox model update a few months ago.
In reality, we can't really know how perfectly nostr clients construct the feed using the Outbox model. Since most people designate at least one large, popular relay as their outbox relay, it would be difficult to notice if a client doesn't actually support the Outbox model.
As a side note, nostr:nprofile1qqsraldwhvwcjgltmxwfu7kw8dqef2692yhzheuurd7k3kfy8cxjdqgpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhszxthwden5te0wajkccm0d4jjumn0wd68ytnhd9hx2tcpzemhxue69uhk2er9dchxummnw3ezumrpdejz7n4mh2x android was the only one that worked even when the internet connection was completely severed. This must be due to it fetching the feed from a local database rather than a relay, building the feed, and continuing to accumulate data in the local DB in the background. It's fast, too.