I used SOFI for mine and had a great experience. My loans are older and interest rates were higher then than what they are now, and, in fairness, I was consolidating both private and Federal loans. SOFI does offer some of the "protections" you get with Navient/Sallie Mae in terms of deferment options. I can't sing their praises enough in terms of ease, speed, and for me, cost. Also, if you take out a mortgage or refi with them and you have student loans with them, you get a .125% interest rate reduction on the new loan. Great if you're buying a house.
BUT, we lost one big benefit: My DH works for the federal government and is therefore eligible for loan forgiveness after 10 years of service. In order to qualify for that program, you have to be on an income-based repayment plan. Typically, your spouse's Federal loans can count in the calculation they do to figure out your monthly payment. However, because mine are no longer Federal loans, they don't count towards our calculation. (To be clear, spouse loans aren't forgiven as part of the federal service loan forgiveness plan... they're just considered in what you can afford monthly when calculating IBR payments.)
We looked at refinancing DH's loans with SOFI, and while the payments would have been lower, there's something to be said for the benefit of loan forgiveness at the end of 10 years, so we left his alone.