If a photographer is asking such a question, then most likely he has little experience so far. Therefore, we will proceed from the fact that a lens is needed for all occasions. But absolutely universal lenses do not exist. Even very expensive ones.
For example, if a lens boasts a perfect picture, it will fixed lens... The downside will be less functionality and convenience. When we buy a zoom, we always sacrifice aperture and image quality to a certain extent. In order to understand what is more important for a particular photographer, you need to gain experience in shooting. And it's better to start with zooms, tk. they provide an opportunity to compare and feel different focal lengths.
This is the lens I would recommend starting with. First, it is very inexpensive. Its price / quality ratio is very good. It is sharp, compact, and offers a very convenient range of focal lengths over a full frame. This is exactly the model with which it is good to start. And only then it will be possible to determine which focal optics are more in demand and which more serious optics are worth buying.
Someone may ask why not take the first Canon EF 24-105 f4L IS? The fact is that the Canon 24-105 f4L IS is a rather mediocre lens in its class. He does not give bokeh, the aperture is low, the image is boring. Of course, it will be better than Canon EF 24-85 f3.5-4.5 USM, but the price is several times higher. For a trial to decide, it is better to start with a more budgetary model. Then you can already understand for yourself whether it is worth taking Canon EF 24-70 f2.8L or it is better to switch to fixes. Or maybe even leave the Canon EF 24-85 f3.5-4.5 USM for reporting, and shoot for fifty dollars for creativity, which will be discussed later.
50mm full frame is a pretty comfortable focal length. In particular, for work in the studio... But it's not only that. Canon 50mm f1.4 is a very fast lens, but it costs little money. This lens, I believe, should be in any photographer's kit. Excellent image quality, remarkable bokeh and compact dimensions are the main characteristics of Canon fifty dollars.
Never drop Canon 50mm f1.4. This lens is very fragile. Its focusing mechanism is very easy to damage. A ремонт it can cost you half the cost of the lens.
Canon 50mm f1.4 paired with Canon 24-85mm f3.5-4.5 USM will open up a huge scope for the photographer for a creative work for very little money. This is where I would advise you to start mastering the full frame.
In addition. If you buy a Canon camera, my big advice is: buy Canon lenses too. Only they have excellent color rendition and no problems with autofocus. Sigma, Tamron, Tokina - it's all from the evil one. Although I am satisfied Samyang 14mm f2.8 in terms of sharpness, but its color fidelity doesn't match Canon's native lenses.