Both Modern JW's and Bible Students reject the trinity. They also both believe Jesus is Michael the Archangel and in the invisible return of Christ, which is of course only discerned by their group. They both hold to only 144,000 going to heaven. Each claims exclusively to have the only truth and be the only true disciples of Christ. The Bible students believe Christ returned in 1874 and the Witnesses hold to 1914.
The biggest differences are that the Bible students allow blood transfusions and observe all holidays, unlike their cousins the JW's. The modern day JW's reject all of Russell's pymidology charts, and the BS still hold to it. And to the belief that the pyramid of Giza is the "great stone witness" of Jehovah.
I was a witness for 12 years and associated with the BS for about two years after leaving the org. The biggest similarity I saw was that each group although claiming to follow Christ, understood very little of Christ's teachings. Also just like the individual JW worships the Organization and allows the organization to interpret all scripture for them - the Bible Students worship Russell and allow his books to interpret all scripture for them. Niether group trusts in the Holy Spirit to reveal to them as individuals what truth is and both groups will reject you for going against their leader. Again, their leader is not Jesus Christ. Lilly