I have been reading WikiHow and how to become a Muslim, a Christian, and a Jew. It seems to me that becoming a Muslim is fairly easy. You just have to recite and believe a short prayer, read the Koran and other necessary books, learn how to read and speak in Arabic, converse with other pious and knowledgeable Muslims, and do other kind, goodly things. Becoming a Christian seems to be very similar to becoming a Muslim, but it involves an additional step: baptism. In Islam, the new convert would take an immediate shower after saying the prayer to cleanse himself of past sins. Also, deceased children are said to be automatically sent to heaven! In Christianity, there is a problem for unevangelized children. In Christianity, the new convert would probably have to first read a translated version of the Bible (unless the convert understands koine Greek and Hebrew), study which denomination is closest to his interpretation of the scriptures, repent, make an appointment with a priest to conduct a baptism, and be saved. In Judaism, a person has to learn and keep the Torah, worship God, and read the Tanakh. Of the three Abrahamic religions, I think Islam would be the easiest to convert and follow, Christianity second, and Judaism last. Despite that I would consider Judaism hardest to convert and follow, I think anybody who wants to be a Jew must be very disciplined in order to memorize and obey the commandments and restrictions in the Torah. I believe that self-discipline is an important virtue and a way to show one's piety and reverence. Judaism may be difficult to keep undoubtedly, especially all those dietary restrictions. I would admire anyone who would sacrifice life's pleasures (eating any type of food without any feelings of guilt) in exchange for piety, self-discipline, and reverence. Christianity seems to be more laid-back and lenient; however, it may suggest a lack of self-discipline and willingness to adhere to God's laws. What's the purpose of obeying God's laws when not obeying them just means you're going to be "forgiven" or excused? What motivates the Christian to obey God's laws when the laws of the Torah are not required for salvation? That salvation is granted freely to the sinner? What does this say about self-discipline, philosophically?
In order of easiness, not only of conversion but of practice:
Christianity demands that potential converts simply utter a prayer of recognition and submission to Jesus Christ to enter into the Kingdom of Heaven. Views on baptism vary between denominations and even individual churches inside of a denomination. One can be saved, and enter into the glory of God, simply by uttering the simple "I believe you died for my sins, Lord Jesus" on their deathbed. Christians do have commandments that bind them; but these are often downplayed in Churches and emphasis is based upon the "golden rule" to love others as oneself. Further, with absolute and perfect salvation comes the idea that one can no longer sin which causes some Christians to become quite hypocritical in their faith.
Christians believe that obedience to the commandments, and to God, will be instilled in them by their strong faith and belief, as well as by the Holy Spirit taking up residence in their soul/heart.
Islam demands that a potential convert be educated, at least, on the basics of the faith and on the Qur'an before attempting conversion. It is possible to recite the shahadah (statement of faith, it's verbal recitation is required for entry into Islam) and the conversion be deemed ineffectual due to improper education, understanding of the faith and/or the Qur'an, or even because it was not pronounced or done properly. Most of Islam understands and requires that at least two witnesses be present during the initial recitation of the shahadah for a conversion to be legitimate.
Muslims believe that sin is eradicated during conversion; however, sin can be accumulated after conversion. Sin is considered bad and must be actively eradicated through prayer and redemption rituals similar to Judaism's. Most sin comes from actively breaking a commandment. Accidentally breaking a commandment may or may not be considered sinful.
One does not have to learn Arabic to be a good Muslim and, indeed, many Muslims never learn Arabic or complete a pilgrimage. While this is not ideal, it is a fact and exceptions are usually made due to financial situation and/or other concerns in life.
Judaism does not actively proselytize and potential converts are, often, actively dissuaded. If a potential convert is accepted by a mentor, which would be a Rabbi sponsoring their conversion, they begin a life of study and preparation. Once one converts into Judaism there is no going back and one must follow all of the commandments all of the time. In Islam one is excused from many commandments while they learn of them; but in Judaism you are not excused from even the least-most commandment from the moment you rise from the mikveh.
Potential converts must learn the commandments which pertain to them, must learn to read Hebrew script (even if they do not understand Hebrew), must convert to kasher eating, and so on, before they are allowed to convert. Orthodox conversions require the potential convert to move into a Jewish community and their home must be open for inspection.
The potential convert faces a beit din (House of Judgement), a Jewish court of Law, when they are ready to convert. They must demonstrate knowledge of Hebrew, read in Hebrew, and answer many questions including, but not limited to: why one wishes to convert, what one hopes to achieve from conversion, how long one has studied for conversion, and so on. They must also demonstrate knowledge of the mitzvot (commandments), how they are to follow mitzvot that pertain to them, and what should be done if they have sinned.
Hope that helped!