After looking over the 14 deals, I've come up with what I consider to be the best for the Cubs, the worst, and the splashiest.
Ron Santo for Steve Stone, Ken Frailing Jim Kremmel, and Steve Swisher. This is the splashiest because of Ron Santo. Sending one of your biggest names to the cross town rival is a big deal.
What always struck me as odd about this trade is that the Cubs got four players for one. Santo had earlier vetoed a trade to the Angels, saying he wanted to stay close to his Chicago home. That didn't leave the Cubs too many trading partners. I would have thought the White Sox could have gotten him for practically nothing, knowing the Cubs had few other options. But the Cubs were able to wrangle four players from the Sox.
The Cubs were in a pennant race in 1998 and looked to the White Sox to bolster their bullpen. The got reliever Matt Karchner in exchange for prospect Jon Garland. Karchner had an ERA over 5, not exactly bolstering the bullpen. Garland helped the White Sox to the 2005 World Series title.