I've done both.

It really depends on your age and what your life objectives are. I paid off my mortgage in my early 40s and ended up regretting it to certain extent - should have paid into my pension pot and got the tax benefits and growth.

On the other hand it's nice to have zero debt!

Just recently bought a bigger house after renting. Mortgage is same as rent was, but house has a self contained room for renting out. It's a new build and energy efficient. I have no plans to pay down mortgage right now as fixed on 1.44%. I love the freedom having lots of cash gives you.