I would go for TransactionScope, because it's much simpler to use, as you don't need to carry over a transaction object, or pass it to every method. It's ambient. It means, most of the time, developers can almost forget about transactions, write cool business-oriented methods, and then, later, add transaction wrappers (using 'using') where it's really needed, afterwards. (sounds idyllic I know, but it's almost that).

Contrary to popular belief, using a TransactionScope does not means MSDTC will be involved, see here for a recap on this:

Avoid unwanted Escalation to Distributed Transactions

And, if you really need to have a distributed transaction, well, how do you plan to do it without MSDTC anyway? What's interesting with TransactionScope again, is it will escalate to MSDTC if needed, without changing nothing in your code.