How to transfer photos from iphone 4s to 6s? Through itunes or iCloud is okay?

How to transfer photos from iphone 4s to 6s? Through itunes or iCloud is okay?

ICloud is fine, or you can create a backup using iTunes on your computer, then on the 6s, do a restore from the backup

Yes, but using Airdrop between the phones would be much simpler and easier.