I bought pressure mounted gates for the same reason - living in rented accomodation at the time. I think they're good if you've got a fairly "standard" gap (don't ask me what that is!). If your gap is larger, you can buy extension panels (but for one particular spot in my house now, that made a just too small gate just too big!).
I've found gates useful, so they've got freedom to move around, without having to watch them all the time.

Beware using these things if you have walls that aren't made of bionic concrete! We bought some deluxe model from Mothercare to use between bannisters and a load bearing wall. Our house is turn of the century so the walls aren't plaster board as in some new homes, but they are some sort of lathe, plaster and brick mixture and pretty thick. While the accompanying literature warned against the former they made no mention of any other sort of wall. So we started to put up the gate and before we had jacked it up to the required pressure we heard a crunch and looked around to see that the end we weren't concentrating on had just disappeared into the wall. Seeing as we had just had the entire hallway decorated this was kind of annoying. To their credit Mothercare did compensate us, but only after a bit of a battle.
I think you will find that you can adjust the top and bottom pressure points to fit uneven gaps - but don't know by how much. Must be quite a bit to cope with skirting boards though.

We had timber gates made to match the pannelling on the staircase walls, to prevent grandchildren falling down the stairs.
Fixed to one wall with piano hinges, and slide bolt on the other side to lock in place.
Slide bolt was attached to the side that kids couldn't reach - not to say they didn't try. Worked so well that we had similar type of doors fitted to the open plan formal lounge and bar area.
Looked very attractive, kept the kids out of the fromal part of the house, but didn't block the view.
Have just sold that house, and new owners want the doors left insitu

Willow2, could you tell me what kind of stairgate you eventually went for, as I have the same kind of walls, and as you probably know, they are no good to screw into either! Has anyone else had this problem?

Couldn't begin to guess the layout of your house Honeybunny, but in a rented flat we used stairgates purely on the openings of the living room and DS room doors. Used pressure mounted ones, Tomy from Argos catalogue, which were fine.

Ellaroo - we bought the bog standard cheap ones that screw into the wall - we had to screw a bit of wood into the wall first using whacking great big screws, and then screwed the gate on to that. Can't remember the name of them - but they weren't expensive - think about £15 each? They open completely as they're on sprung hinge - which is good as I think the ones that you have to step over a bar to get through are potentially dangerous.

Think I know the ones you mean & thanks for the advice about the trip bar. Am not confident enough about the state of the walls to go anywhere near them with a screwdriver and very big screws myself, so think I will hire in a handy man for the job!