Which has a greater influence on sound quality, the amp or the preamp?

Which is more important to walking? The left or the right leg? 

Not a good analogy.

But as,someone stated a good tube preamp does wonders to enhance the SS amp.

I’ve owned many different mid-fi and high-fi preamps and amps, both SS and tube.  All the components, and the mixture of components, can make a marked difference in sound. I personally like to keep the amp and preamp made by the same manufacturer and, of course, both being tubes.  Also, you must have quality loudspeakers to critically evaluate any changes in your system.

Everything is important but first upgrading the weakest link in your system will have the most influence!

The answer is "yes." How active is the preamp? How passive is the preamp? If there is gain, how is it done? What is the power supply, if there is one? Is there a DAC? Is there a phono preamp with gain? Is there a headphone amp? Are there filters? Is there a tube gain stage? How many dB? Selectable or not? Is there a balanced XLR input or output? On one extreme, you have the minimalist NVA preamp with no gain, all single-end input and output, no power supply. High-quality pot and source selector, a cabinet and that’s all. OTOH, you have a Pro-Ject Pre-Box RS2 with headphone amp, XLR in and out, dual DAC, I2S, USB, multiple filters, selectable tube stage with gain, remote, and a display and all in a cabinet less than half rack width.