I'd tried both of them ,and Gainers Fuel 2500 is better the only bad thing is the taste but u get results in weeks, of course u must have discipline and make some exercise to see the results, but I'll recommend u to try Universal Gain Fast it has better taste and great results I was weighting 139 pounds before trying it (really skinny) and after I was weighting 157 pounds and no fat.
I use Mega Mass every now and then as a quick meal replacement. I don't like chocolate, so I ordered the vanilla, and it doesn't really taste all too good. However, as stated, you can get used to the taste, or just down it in one quick drink. If you can get over the taste, it's hard to beat the stuff for a quick 600+ cals. :thumbup: ~Steve