I think both are around the same power. Granted that Goku had more problems with Metallic, but he wasn't going all out, whereas he gave it all against Blue from the get go. Still, Metallic managed to surprise Goku with his durability and attacks (like the flying hand), so Metallic would likely edge out Blue and win.
Blue displayed far better durability feats than Metallic with him surviving his plane crashing into a mountain, whereas the Goku that Metallic fought was likely comparable to his 21st TB self who displayed nothing close to Large Building level feats. Regardless of how he compares in power, Blue has the durability to outlast Metallic's batteries.