It very much depends on the person you are being mekarev. Some people are intellectual, and they need to sit with someone intelligent who can show them that (a) there are answers, we aren’t just fanatics, and (b) to actually answer the questions. Other people have very little sechel [read: Are not thinking people, are happy to subscribe to belief without a ‘knowledge’ per se] , and are led around by their emotions and good feelings. For these people, the “fluffy-kneidlach-syndrome” is more likely to be effective.
Most people, however, will need a combination. The base desire to become Frum will need some form of rational thought, which directly involves Bikush HaEmes. But commitment can only come if negative connotations associated with Yiddishkeit are dispelled, and that is best done through unconditional warmth, acceptance and love. Appealing to both emotions and intellect together is the surest way to motivate someone to take the leap.
Another point – to many people, a well delivered intellectual lecture can appeal to the emotions as well, not just to the intelect.