According to the entry in Wikipedia about WPA:
"
TKIP (Temporal Key Integrity Protocol) The
RC4 stream cipher is used with a 128-bit per-packet key, meaning that it dynamically generates a new key for each packet. Used by WPA.
CCMP (Counter Cipher Mode with block chaining message authentication code Protocol) An AES-based encryption mechanism that is stronger than TKIP. Used by WPA2. Among informal names are "AES" and "AES-CCMP". According to the 802.11n specification, this encryption protocol must be used to achieve the fast
802.11n high bitrate schemes, though not all implementations enforce this.[SUP]
[24][/SUP] Otherwise, the data rate will not exceed 54 MBit/s."
I take this to mean that AES might be needed to achieve wifi data transmission rates on a router that exceed 54 MBPS. However, it seems that shouldn't necessarily impact internet speeds, since the average good internet provider gives download speeds of around 30 MBPS.
I'm not sure why you needed to change your router from AES to TKIP, although as I mention in that guide, this can sometimes help solve connectivity problems. AES is a stronger encryption than TKIP, so obviously AES would be preferable. Do you have multiple access points in your house using multiple routers? If so make sure all of them are using the same encryption protocol.