My daughters both have AS and have both been on Methotrexate. They were both on MTX in combination with an anti-TNF though - not by itself. My younger daughter had a lot of side effects with MTX - nausea, dizziness, fatigue - but my older one had no trouble with it at all. It really depends on the person.
My younger daughter took Zofran for the nausea. They both took Folic Acid and that helped prevent side effects. They both did the MTX shots on the weekend so that they had some time to recover. They both did better on shots (vs. pills) but some people do better with pills.
MTX worked very well for both my girls. It was meant to help more with peripheral joints - most studies show that it does not help much with spinal/axial AS. We hoped that it would help their knees, ankles, elbows, feet etc. but both say that they think it helped their SI joints and lower back too.
Typically if MTX does not work, an anti-TNF like Remicade or Humira is used, especially when the spine and SI joints are involved.
Good luck!