Spire of the Sunless
Bifrost is definitely a ‘better’ weapon in terms of utility, as it can switch to any stat you want, and has all the upgrade and infusion slots you would have on an ascended weapon.
The only difference is whether you prefer the look. I do have to warn you though that if you use Bifrost, your autoattack on any element becomes just a rainbow something instead of fireballs/water sprays/lightning bolts/rocks, which is a pretty stupid change cosmetically.
Rampager (these are teq stats’ aren’t they?) isn’t a good choice for ele, you will not have a role where bonus stats from ascended quality will outpower right combination from usual exotic (like berserk or pvt). So give it to your necro or something.