I have tried ubuntu on mobile only once and never come back, because it had very bad and poor experience compared to native experience of that mobile. On which models this system works the best?

GrapheneOS is highly usable and compatible with nearly all Android apps. It has a similar experience to a mainstream Android OS if you choose to set it up that way such as using sandboxed Google Play in the main profile (which does not ruin what it provides at all, it's a perfectly valid setup). The purpose of GrapheneOS is to provide far better privacy and security than the Android Open Source Project (AOSP). AOSP is a lot more private and secure than a traditional desktop OS including one ported to mobile.

See https://grapheneos.org/faq#recommended-devices for the device recommendations. There are going to be Motorola devices with GrapheneOS support within a year too.