I recently spoke with a colleague who transitioned from Juniper to Cisco. We agreed that each solutions is completely different and each one has its strong and weak points.
The transition process was rather hard. It was hard to change approach and rare similarities were sometimes misleading for my colleague. Although Cisco is moving away from the standard monolithic IOS straight to modular architecture there are many disadvantages for somebody who 'thinks modular'.
Personally I have experience with Cisco and although I have some difficulties and a Cisco-centric way of thinking, I prefer it over the others. But if I would possibility need to be involved in a Juniper environment, I think it would be worth to walk through the transition process.