The decision to use weldable or boltable clips should be based on local site conditions such as accessibility to the underside of the girder, site safety for installation personnel, existing bolt holes, etc.
A weldable clip, with removable fixing bolt inserted and removed from above, is much easier to install and dismantle than a boltable clip which requires access from both the top and beneath the rail support girder or soleplate.
Regarding safety, because it is more dangerous when working in high places, installing boltable clips requires movement of the installer and access to both the head of the bolt as well as to the nut.
Some standards penalize a weldable type solution, by imposing flange thicknesses much more significant than those required for boltable clips. Some national practices forbid welding clips on girder aisles.
Boltable clips can be supplied as 100% protected by hot dip galvanization : a major advantage against corrosive atmospheres.