It's too late to update my original comment, but here are the fastest 128-bit key implementations of AES, Simon, and Speck for the AVR processor according to the CryptoLUX group at the University of Luxembourg:
The differences look insignificant. Code size and RAM requirements are in bytes (not megabytes). In fact, AES might be faster than Simon because the AES encrypts a 128-byte block whereas both Simon and Speck encrypt a 64-byte block; therefore you'd have to encrypt two Simon blocks to get the equivalent of one AES encryption.
AES> code: 2588 bytes; RAM: 208 bytes; encrypt: 2835 cycles
Simon> code: 972 bytes; RAM: 200 bytes; encrypt: 1793 cycles
Speck> code: 1426 bytes; RAM: 132 bytes; encrypt: 997 cycles
The differences look insignificant. Code size and RAM requirements are in bytes (not megabytes). In fact, AES might be faster than Simon because the AES encrypts a 128-byte block whereas both Simon and Speck encrypt a 64-byte block; therefore you'd have to encrypt two Simon blocks to get the equivalent of one AES encryption.