What piercing branch connector is better- ОВ or ОВ-Т?

They are both piercing branch connectors, so there is no need to cut a cable and remove insulation. OB-T has several advantages, the main of which is that there is no need to connect a cable at the moment of installation of this branch connector. You can leave them assembled on the cable until the moment when you will need to connect another cable with the help of a male disconnector. They are smaller, so more compact and less expensive.