*edit* sorry.... I mean to post this on this thread, but accidently posted it on another I was reading.*
Its easy to say that some composers were better at composition than others....
like Bach being better than Telemann, Mozart better than Salieri (hehe... Amadeus), etc. Although Chopin and Liszt were contemporaries, it is really very hard to judge them against each other. For one thing, Chopin died in 1849 and Liszt in 1886, so obviously Liszt had more time to perfect his craft. Chopin wrote really great music... keeping in mind he did this all under the age of 39. Liszt by comparision, would have been very busy touring as a concert pianist from age 25 to 35 so.... by the time Liszt was 39 certainly Chopin's music was more developed, in a more mature style than Liszt. But Liszt did not stay the same - his music drastically evolves as he ages. After Chopin's death, Liszt begins to embark on some very, very big compositional projects. He wrote ochestral standards like "Les Preludes" and his piano concertos.... and massive piano works like his Sonata, and the Annes de Pelerinage. He also wrote large choral works. Music was Liszt's life- he truly believed in the power of music and kept writing, improving, and experimenting up to his death. It is sad that Chopin did not live beyond age 39, because he would surely have given us some great music - composers tend to write their best later in life. Yet for such a short life, Chopin created music that far surpasses some of his longer lived predecessors.
In the end.... you cannot compare them fairly, just as you cannot compare Bach and Stravinsky fairly. So instead of asking "Chopin or Liszt?" you should be saying "Chopin and Liszt!"