E6 transparency film has less exposure latitude and film labs which can process it are usually only found in larger towns and cities. If one is currently, or is planning to do ones own scanning, then the choice is simple. Transparencies win hands-down in terms of scanning ease. The orange mask in colour negative film, while easing traditional printing issues, complicates scanning. Otherwise the choice comes down to personal work style and convenience.
Chromes are easier to review.
It's hard to beat examining slides on a light box with a high quality loupe. Negs require that small prints or contact sheets be made. Contacts don't tell much and wallet-sized prints are subject to the whims of the lab making them. Matching prints and negs and archiving them is also problematic. Finally, if work is going to be submitted for publication, printers much prefer to work from transparencies rather than negatives, though digital files are replacing both as the preferred media for publication.