How big is your location? How much sun? What else will be planted with/around the tree? These are two very different trees with different looks. If you're planting in a sunny rock garden Shaina is definitely the best bet. If you have a Japanese style garden, or a more traditional garden, Beni maiko may be best. We need more info to help you out properly...

Regards,
K4

Of those two varieties, I think Shaina would be smaller and more compact. Shaina will keep a very deep red color in the leaves if grown in sun. It's form is rather stiffly upright despite its small size. Shaina would handle sun better than Beni maiko.