You won't notice any difference using esata from internal as long as the power is on for the esata.
If the external is not being moved around or in a position to get knocked around it should be just as reliable.
On the other hand an esata external drive is more expensive then an internal sata drive. 1tb internel drives are quite cheap, external 1tb usb are also reasonable, but esata in any size seem a bit pricey, I can get 2 1tb internal drives for the price of 1 esata drive.
You may be able to get a better deal where you are.