ICSI has a higher success rate but there can be higher rates of genetically abnormal embryos because fertilization is "forced".
This explains it pretty well: http://attainfertility.com/article/icsi-procedure
For us, we've had one (probably two) miscarriages and DH has a disease that can affect sperm quality. With a 50/50 ICSI/traditional route, we'll hopefully be able to tell if the issue is egg quality or sperm quality. If all the traditional fert group has issues, we'll know that it's an EQ issue, whereas if the ICSI'ed embryos are abnormal we will be able to discern a problem with sperm quality.