Basic Training = "Normal" Basic Training
The US Army only has two forms of entry level training for new soldiers:
Like the name says, it's basic entry level training for soldiers. Usually done for non-combat arms MOS jobs. Followed by AIT (Advanced Individual Training). The length depends on your job.
OSUT = One Station Unit Training
Used for combat arms MOS soldiers. It's a combination of Basic and AIT all done together at the same location. Essentially it's like Basic Training for 19 weeks or so, depending on your MOS.
As far as "difficulty" goes, it depends. Are you talking physical, mental, or both?
As a rule, OSUT is much more difficult physically and mentally than Basic/AIT. Since you're pretty much locked down the entire cycle, it's like four plus months of Basic, but since it's to prepare you for a combat arms job, it's good training. It's not as physical as it was since kids nowadays can't handle the physical stuff since they spend most of their time on computers, watching TV, playing video games, etc.
Basic isn't that difficult and is much shorter.
Ex-US Army Cav Scout NCO & Instructor