I remember when reading through the graduate stats for the various service-lines the starting salaries were basically the same across all areas, only more broadly speaking were there some differences whereby I'm pretty sure marketing and HR were a bit lower and actuary was a bit higher.
Even the areas you've listed are really broad though, so personally I'd need a bit more detail as to the clients and what type of work in for example taxation (corporate, transfer pricing, government) the place/firm you've gained a position at offer?
Edit, sorry didn't read that this was for a cadetship. Hmmmm, if you're interested more in client relationships and don't mind a bit of travel I'd probably say business services would be the most fun; auditing as others have said is quite broad and will have you working on a range of problems and different scenarios which is challenging and good, taxation can be interesting suprisingly and is good if you are a bit of a wordsmith and don't just want to be a number cruncher (as you'll be drawing on law & statutes); insolvency I don't think much of personally, but there's not denying the money in it.