Rakesh - that depends on a number of factors. Historically, seminal articles were often a single author - take Einstein, Hawkins etc. Nowadays - there is often suspicion and reviewers are hesitant about single-author papers - especially because of potential bias etc. Research-based articles, today, are more likely to have multiple authors (although that could be less likely with qualitative studies). However, conceptual articles, literature reviews etc are more amenable to single authorship.
If you are referring to evidence-based practice I, personally, would be far more hesitant to accept evidence from single-author studies.
Usually yes, multiauthored papers get more citations, but there are some exceptions, see this paper for details: https://doclib.uhasselt.be/dspace/bitstream/1942/822/1/Berlin.PDF