Push fit! I bought a wall screwing one and it came with thousands of bits!! SO i got a push fit lindam one and its brilliant! So simple to fix into place and its stong! My dh fell down stairs when he was poorley and it didnt give way! Highly recommend them!
Only disadvantage of the pushfit ones is that you have to step over a bar at the bottom which can be a bit of a trip hazard.
We went for the screw into the wall ones and it did take dh a while to fit them but we are very happy with them (and expect to have them up for a while as dc2 arriving soon . They also fit the shape of the banisters on our stairs which the pushfit ones we were given didn't (cylindrical posts at top and bottom)
An advantage of the pushfit ones is that you can easily move them to fit in doorways etc if you need to so more flexible.
I had push fit. It was fine, never gave way. My friend is using it now! The only thing was, when we moved house and took it off, a bit of plaster came off the wall with it. the screw in ones would leave a hole anyway though!