Sold my 6x6 101 a couple of years ago having driven it around West Africa.
http://westafrica2006.blogspot.com for details.
For: 1970s mechanicals, spares generally very easy to get hold of, easy to repair when it breaks down (which mine did on about 13 occasions), plenty of room inside (double bed in my 6x6).
Against: not very comfortable to drive, slow, hideous economy with V8 (mine was coming at about 5 1/2 tonnes fully laden, so no surprises there).
I've not used a C303 but I do kinda fancy one. They're a bit smaller but you can buy a purpose-built 6x6 instead of a converted one if you want the extra space. I suspect that spares would be the biggest headache when expeditioning.