What is the best alternative to Google Assistant on iPhone?

Amazon Alexa, S tier, #1 in voice assistant.

Is there a free alternative to Google Assistant?

Yes: Amazon Alexa (S tier, #1) is free to download, with in-app purchases.

Yes. 2 apps rank above it in voice assistant: Amazon Alexa (#1), Jarvis - Voice AI Assistant (#2).

Google Assistant is A tier, #3 of 7 in voice assistant. Here is everything that competes with it on iPhone, in tier order.

1
Amazon AlexaShigher tier
Free + IAP · ★ 4.5 · 5,919,701 ratings · score 97
Companion app to manage Alexa-enabled devices, control music, view lists, reminders and timers, and use Drop In and…
2
Jarvis - Voice AI AssistantShigher tier
Free · ★ 4.9 · 162 ratings · score 89
A voice-first AI assistant that talks with you and remembers details for future conversations.
4
Voice Control - AI AssistantB
Free + IAP · ★ 4.3 · 40 ratings · score 76
Voice control app for iPhone with an AI chat assistant, real-time dictation in 50+ languages, and smart voice commands.
5
SoundHound Chat AI AppB
Free + IAP · ★ 4.5 · 894 ratings · score 71
A voice-based conversational AI assistant for questions, follow-ups, and real-time information.
6
Yandex with Alice AIC
Free · ★ 4.5 · 27,158 ratings · score 69
Yandex app with the Alice voice assistant, text and voice search, a smart camera, caller ID, price comparison, and…
7
AI Assistant: Voice ChatbotF
Free + IAP · ★ n/a · 0 ratings · score 46
An AI assistant for voice and text chat, writing, translation, summaries, and everyday tasks.

What is the best alternative to Google Assistant on iPhone?: Amazon Alexa, S tier, #1 in voice assistant.
Is there a free alternative to Google Assistant?: Yes: Amazon Alexa (S tier, #1) is free to download, with in-app purchases.
Does anything rank above Google Assistant?: Yes. 2 apps rank above it in voice assistant: Amazon Alexa (#1), Jarvis - Voice AI Assistant (#2).