This is/can be, a complicated subject. Far and away the safest and most convenient jack is a hydraulic bottle jack. Small, simple, lifts, holds and usually comes in a sturdy plastic case. But only lifts a few inches. If you're only lifting one side of a motor home or TT get a bottle jack that will fit under the axle at or near the spring shackle. The lift pad on top of the jack will screw out with your fingers to extend the jack (ram) to it's maximum height. Even that might not be enough to get the wheel off the ground given the short stroke of the jack and you might need to put some blocking, short pieces of 2 X 4 or 2 X 6 under the jack before you start to lift. You'll never get it off the ground with a bottle jack if you try to lift it at the frame. Not enough stroke on the ram. If you have to lift from the frame, first, last and several times in between remember that lifting a load is dangerous and lifting by the frame is EXTREAMLY DANGEROUS! The jack you would need if you must lift from the frame is called a farm jack. Harbor Freight sells the one I have for less than sixty bucks. Fit and finish, not so good, value and function, excellent. And they call it the widow maker for a very good reason. If you decide you need a farm jack read and follow the very spirit of the instructions. Practice with what ever jack you decide on well in advance of when you need to use it. As to the jack stands buy good ones. Again Harbour Freight sells pretty good ones for a good price. What ever you get make sure you buy stands that are cast, not sheet metal. The sheet metal ones are sufficient if you need to hold up a riding lawn mower. And last, NEVER, NEVER, EVER! FAIL TO SET THE PARKING BRAKE AND CHOCK THE OFF SIDE WHEELS. Even if the vechiel is in your driveway and you're practising useing your jack.
I don't mean to scare you with all this. I do mean to emphasize how serious useing a jack is. For our own rig we have road side assistance in case we have a serious mechanical problem or flat along side the highway. We carry the farm jack and jack stands for the service I can do and in case of a last resort problem that requires lifting the motor home.
Be safe, do good work and keep in touch.
2002 Designer 3230