ratio of pmos nmos width =2
The reason you would find a beta ratio equal to 1 in some instances is because, when the transmission gate is turned-on, both the pmos and nmos are turned on and are in parallel. Even though only the pfet is good at passing '1' and nfet is good at passing '0', they do pass the opposite logic level weakly. So, together the average resistance is lower than having only one FET on. So, you don't really need a beta=2 like in an inverter but something like 1.5 or 1 is sufficient.