I don't know about best innings, but best performance in a match by far has to be Andy Flower
HowSTAT! Match Scorecard
South Africa notched up 600/3d with Flower keeping wicket. He then came in when Zimbabwe were 51/3 and scored 142 and was last out for the final total of 286. He then had a brief rest as Zimbabwe followed-on, but brief was about the size of it as Zimbabwe were 25/3 in the 2nd innings when he returned to the crease. This time, having been out in the field keeping or batting for all but 76 runs of the match, he made 199no out of the total of 391 which forced South Africa to bat again. They knocked off the 79 runs for the loss of one wicket, Flower was MOTM naturally but to keep and make 142 and 199no in a losing cause is phenomenal. Anyone fancies looking up the time he spent at the crease and in the field, be my guest.
For me he is a legend, not because of his now-England links, but because he played for a weaker Test country, kept wicket and managed to average 50 with the bat. Girly for the aussies gets all the accolades, but how often did he have to bat at three down for less than 100 having kept wicket for a side that regularly lost and conceded big scores??!?!? Not sure he's a good coach, but he's one of my favourite keepers along with Adam Parore who I believe holds the record for most runs scored without conceding a bye