My family and I were practicing Muslims for quite a while and, currently, are in the process of formally joined the Catholic Church. In answer to your question, I cannot only speak for myself (as opposed to my wife).
I can summarize my reasons to convert, briefly.
The Catholic faith is reasonable. More specifically, faith, that is known by revelation, is NOT incompatible with reason, that is engaged through the senses. Islam, on the other hand, presents God as pure will. God, in Islam, can never truly be known. He is Other. Consequently, an orthodox Sunni Muslim cannot say that faith is reasonable. For example, one can ask if alcohol consumption is essentially immoral or is the abuse of alcohol. Ultimately, a Muslim must insist that ANY alcohol comsumption is immoral, because God said so. This approach, which was solidified in the 14 century, locks Sunni Islam into legalism. Alcohol is forbidden in Islam because it potentially causes one to ask inappropriately. On this basis, soft drinks (or automobiles, etc) should be forbidden due to potential health risks. Sunni Islam turns out to be Divine legal positivism.
This is the single largest factor for me. Basically, the Catholic world view is consistent and clear, despite those Catholics who openly dissent. This leads me to the largest stumbling block to Catholicism for me…Catholics