depends if you're picking on talent and enjoyment of watching or purely on result. if you're going for result then obviously the man with the greater ouput is the better pick, the one who has got his team out of the most jams in those tough situations. i think kallis gets a bit overlooked because people see him more of a slower batsman but if you watch him play you'll see he's got some of the best cover drives you'll have ever seen and is so in control of them it's ridiculous, almost like he's batting against school boys. also depends if it's a one-off match or a series or a team touring for a year...maybe you'd take tendulkar in a one-off match, for a tour or longer maybe kallis...
All Time Test XI: 1 Hobbs 2 B.Richards 3 Bradman 4 Pollock 5 V.Richards 6 Sobers 7 Gilchrist 8 Procter 9 Miller 10 Marshall 11 Warne