It's neither. The very beginning has vocals panned center, a low distorted sound in the left channel, and a low non-distorted but very compressed sound in the right channel (plus a shaker panned slightly right). Those are two different instruments playing the same part. Part of the giveaway is after the first half of the first verse (ending with "...in this life") staccato chords begin panned right, which are almost certainly an organ, most likely a Hammond B3.
That validates the idea that at the very beginning, the left channel sound really sounds like a B3 with a lot of distortion on it, like Deep Purple used to have (think of the intro to Smoke On The Water which is played on distorted B3).
Then the other instrument in the right channel is probably a bass guitar that is very compressed or possibly using a bass synth sound. It's possible that it is another keyboard track or a double of the B3 part, but the band did have a bass player during the recording of that album and it's unlikely there would be no bass on that song.