It really depends on what that one knife is for! I don't have the FG, but have a few TGULBs, and I love it. For general use, TGULBs for sure over the mega Ratweiler. The Mega Rat is a beast. Cool beast! But I wouldn't want to carry the weight all the time. However, if I we're splitting coconuts, making Pina coladas all day for a living, it'll beat the TGULB hands down. The Mega Ratweiler blade design will split like it's nobody's business.
They're both tougher than nails, so I'm not worried. SR-101 and INFI are both great steels to have!