The main difference between capital classified as Tier $1$ versus Tier $2$ is that

Tier $1$ capital is more liquid and can be sold more easily

Tier $1$ capital pays a higher rate of return to shareholders than Tier $2$ capital

Tier $1$ capital is more likely to be available to absorb losses of the bank

Tier $1$ capital has a finite maturity while Tier $2$ capital is perpetual