The LG does not have freesync, where as the Samsung does. If you really need freesync then go for the Samsung. The Samsung also has a 4ms response time compared to the LG 5ms response time.
However, the Samsung is 1920x1080, compared the the LG's 2560x1080 ultra wide screen. So you'll be downgrading in resolution. The LG is also an IPS panel, compared to the Samsung's SVA. An IPS panel is much more colorful and vibrant than SVA.
All in all, it's better to just keep the LG and save up on upgrading other components in your system.