This is a very difficult question to answer, but one of the most common. The overall conclusion of a few studies is that they appear to be very similar with respect to complication rates. The best we can do is look to several recent journal articles investigating this question. However, it is very important to note that there have not yet been any well-designed studies (randomized, controlled trial) to specifically address this question.
1. Nasr, A., Fecteau, A., & Wales, P. W. (2010). Comparison of the Nuss and the Ravitch procedure for pectus excavatum repair: a meta-analysis. Journal of pediatric surgery, 45(5), 880-886.
Unfortunately, in this review, there were no identified randomized trials (gold standard clinical trial type) comparing Nuss and Ravitch. Yet, in a series of non-randomized trials, the authors compiled together lots of data and determined no difference in the rate of complications seen in Ravitch and Nuss. However, they found that the Nuss procedure leads to more bar migration or more persistent deformities. For specific complications, they also found higher rates of pneumothorax and hemothorax with the Nuss procedure. The Ravitch led to longer surgeries but they both led to similar hospital stays and recovery times.
2. Kanagaratnam, A., Phan, S., Tchantchaleishvilli, V., & Phan, K. (2016). Ravitch versus Nuss procedure for pectus excavatum: systematic review and meta-analysis. Annals of cardiothoracic surgery, 5(5), 409.
In this more recent study, the authors compared 1,432 PE patients (912 Nuss and 520 Ravitch), taken from a total of 13 separate studies. When combining the data, they found no differences with respect to complication rates, reoperation, wound infections, hemothorax, pneumothorax, or pneumonia.
3. Mao, Y. Z., Tang, S., & Li, S. (2017). Comparison of the Nuss versus Ravitch procedure for pectus excavatum repair: an updated meta-analysis. Journal of Pediatric Surgery.
This is the most recent study to investigate the question. They specifically were interested in amount of blood loss. They found 19 studies (1731 patients total, 989 Nuss and 742 Ravitch). Overall, the Nuss patients appeared to have shorter operation time and more blood loss. The hospital stay was similar for both.