Red Ear Slider most likely. Listen very carefully to me on these next points. These things will get big, they will require a big tank, and it will require a ton of time to maintain. It will not stay quarter-sized forever. They are not pets that you pick up and hold. (Many have salmonella and they are aggressive.) You need to have a filter and a special heat lamp for these turtles. You must have a dock of some sort so they can get out of the water to bask. Every week you need to completely empty their tank and scrub it down. This species needs to have deep water, so you can't just put less water in to avoid all the work. If you get tired of this turtle and want to let it go, you better make damn well sure that they are native to the area. Red Ear Sliders are known to be incredibly invasive and can wipe out local turtle populations by outcompeting them. Don't be part of the problem OP. It's not all bad though. Turtles can be interesting pets to look at, and will start to recognize their owners and come to the tank's front around feeding time. Their's a ton of work involved, but it can be really rewarding.