Are there any better alternatives than donepezil to treat alzheimer's?

Maybe. "better alternatives" is in the eye of the beholder. Currently, drugs approved to treat alzheimer's disease only slow down progression but don't necessarily restore memory & cognitive function. Donepezil, galantamine (galantamine hydrobromide) & rivastigmine are cholinesterase inhibitors while Namenda is an nmda receptor antagonist. In truth, no study has demonstrated that any drug is better than the rest.
Donepezil. Unfortunately the current number of drugs to help treat alzheimer disease is limited. Although some drugs beside donepezil may show some benefits in some patients, these therapies remain unproven.