I used to be an avid collector of both, infact I was something of an addict; I've still got about three years worth of each stacked away in my loft. But as soon as I fell out of love it was instantaneous, I just dropped the habit and never went back. If you're a fan of mainstream, populist filmmaking, or semi-famous cult filmmaking/makers then they will obviously both appeal to you, but if you are more interested in viewing the cinema as a serious art form, then Sight and Sound (or even Film Review, at a stretch) is for you; their analyses are likely to be more thorough and more focused on the artistic merits of a film, than either of the aforementioned, would be.
To be honest, I haven't read a film magazine in ages (mainly because none of them totally satisfied me), so I'm not that well informed on the current issues, but from experience there really is nothing to separate the two, except that Total Film had a bit more creativity to it (particularly with those interest graphs they used to do) and more scope in giving out marks (i.e. out of ten rather than out of 5 stars.) They both tend to appeal to the teens-to-early-thirties lads demographic and if you fall outside that area, or have different tastes to theirs, it's very possible to end up feeling alienated by them. Also, it's rumoured that studio influence holds sway over their critical judgements (whether this has any founding or not, I once heard that a studio would require a favourable review of a movie otherwise they would have no interview or cover feature with it's A-list star.) And Empire will never slag off Star Wars: they were a bit critical of it once and, as a result, ended up getting swarms of letters from angry fans moaning about it.