I don't see the harm in applying for both, as long as you realistically feel you have the skills or the ability to develop the skills for each job. I don't really get the 'serial applier' that some people say, in fact I have heard quite the opposite from HR (other company) and that it shows you are keen to work for the company also lets face it jobs can be few and far between that you feel you could be really suited too, especially driving jobs, so why wouldn't someone apply for both?
I've got 5 applications in with northern at the minute and I have progressed with two of those for online testing and I read on this forum that northern only accept one active application so I wouldn't believe everything you read on here. Also with TfW I put in for two positions at the same time - one was rejected and I am in a talent pool for the other so they musn't have frowned upon applying for more than one position. I say go for it but choice is ultimately yours!