We used a BabyDan portable one in DS's doorway for a while - useful if you want to avoid permanent fixtures - you just move the whole thing out the way to get past, so good for containing child for a few minutes, but not good for anywhere you will be frequently opening and closing.
For the actual stairs we had the BabyDan No Trip gates (I think). They have to be screwed to the wall / bannisters (don't think you can avoid this if you want one without a bar), but ours have been down for a couple of years and you don't really notice the holes. They open quite easily, and the gate swings back fully, so no squeezing through a gap you can't see properly while carrying a load of washing or whatever.
We have a Lindam extendable for the top and bottom of the stairs as our stairs are quite wide. Easy to open and close and opens wide.
No bar across the bottom to trip on. It screws into the wall. Our thinking was DD is only 11mths now and we will be planning number 2 in a while so will be up for quite a few years so needed something sturdy.