Interesting to see everyones take on this question. For me the answer is easy. I have the I-pilot and 2 side scan units and really like them all but I would rather have the SI if I could only have one. Here is why: With the SI I can easily find the structure or cover I want to fish and even decide which ones to fish by the numbers I fish I see on it. I could not do this with a normal depth finder very well. As for I -pilot it is nice to have the advanced functions like advanced auto pilot, cruise control and spot lock but I can do these things just a well with a regular trolling motor it just takes a little more work. As for running routes I can use a few small marker buoys to layout a route to follow. Very often I do not engage the advanced functions of I-pilot because i can do just a well without them. In short SI puts more fish in my boat than I -pilot and SI functions cannot easily be replaced with a normal depth finder where I -pilot functions can with a handheld GPS.