Arduino the -best- choice? In what terms?
It should be sufficient. It doesn't take much CPU power to keep up with input from a person.
There are a -lot- of alternatives to ATMega. PIC, Propeller, TI, ST, Freescale, Si Labs, etc. and more etc. It seems like just about every IC manufacturer has their own microcontroller.
For price, TI has an ultralow power 16 bit MCU, the MSP430, some versions way under one US dollar. The Propeller has 8 cores in an 80MHz chip for $8.