Both. Each has their own place.
Monopods are ideal for supporting the weight of a camera and lens for extended periods, often where slow shutter speed isn't necessarily the problem - but of course it can assist stabilising the camera when conditions or artistic requirements mean slowing shutter speed to levels where camera shake can be a problem.
Tripods are ideal for situations where a long shutter speed is required - landscape photography, product photography etc.,
There are those who eschew monopods and take macho delight in handholding heavy equipment all day. My take on it is that I've only got one spine and its got to last me the rest of my life, and taking care of it now is likely to pay dividends later in life.
My monopods are conventional with a single rubber foot.
If you find your lens heavy after extended use, a monopod may well help - but they do take a bit of getting used to, sometimes you'll unclip it from the monopod as waving around a 5 foot metal pole at 90 degrees to the camera isn't practical. For that reason, I have a head that uses the same QR plates as my tripod - and for balance purposes, many heavier lenses come with tripod / monopod mounting collars.