Well, the Antonov 225 Mriya is the heaviest airplane with MTOW around 640 tones. Quite impressive ,considering the 747 400 ER with 412 tones MTOW, or the A380F with 590 tones.
The A340 HGW 9high gross weight) has a MTOW of 380 tones..
Also ,the B 777 F has a MTOW of 347 tones.
You may say that Mriya rules,and it will do so for some time.