when it comes to Junipers market share in service providers space and enterprise security space, its not because of sheer luck, I am not sure how technical you are : but
junipers product line is far superior than cisco.they are too advanced, scalabale, consumes much less power, one super great operating system thru out the product lines, yes even the security gateways and the new switches they are releasing will have junos.

so this is my take:
Cisco has a lot of muscle than Juniper.
Cisco has loads of other products than Juniper offers.

but otherwise:
Juniper products are far superior, easy to maintain and use, better ROI than cisco.
Juniper didnt learn the dirty politics that Cisco
employs when it comes to marketing/sales of their
products.