That is difficult to answer because there are so many different guns in Apex Legends. However, a few of the best weapons for beginners include;
The Peacekeeper - This gun can be found on some of the larger maps with lots of high ground and plenty of room to move around. The Peacekeeper also has one of the highest damage per magazine ratios which makes it very effective against players who use shields or body armor effectively.
LA7 Rebel - With a low rate-of-fire and small capacity this weapon really only works at medium range but its large magazine allows you get off quite a bit more shots than other similar weapons without reloading often