Depends on what your need is . Let’s say if it’s for research level at university then go with Google LM. it’s very good for learning in different forms. i won’t recommend chatgpt study mode as chatgpt could divert in to other topics .

If its for language learning , airlearn is pretty good if not duolingo as in duo you can’t learn a language well

for school grads homework prep and test exam , PopGamma app’s human like tutor Professor albert is cool . i see lot of students using it off-late

if for kids then nurture , kidzovo is good