I do buy all the 3 monthly UK magazines and find they all have their own merits and drawbacks. Railway modeller has a good selection of layouts generally and is good for the swopmeet dates section(even if the bloody organisers don't bother telling them when they change dates that are double booked with the British superbikes). Its also been around since the dawn of time so is well established.
BRM is good for more steam era modelling and the loco building section is second to none, the reviews are also better and more substantial than in railway modeller There are usually a lot more classifieds than the other 2 mags too. If you are ever struggling to get to sleep on a night i find the letters page to be en excellent cure for insomnia but with little constructive to offer on anything.
Model rail is probably the all rounder of the 3 with useful info for beginners and more experienced modellers alike, it doesn't tend to be aimed at steam or diesel in particular but offers a good balance of items on both areas(not forgetting electric and narrow gauge). The masterclasses are very good, its a pity i missed about 2 years worth before i took up modelling in late 2001, the Q&A pages are informative and the letters page is also worth a good read.
There is a 4th mainly UK mag that being Modern Railway Modeller which is by the BRM and traction team, this is quarterly and although it started out brightly enough seems to have lost its way a bit with many articles seeming to lack a bit of depth. I don't really see the need to include a secction on overseas layouts as there are enough magazines devoted to that type of layout, though maybe thats just my opinion because i model UK outline.
This year i have subscrbed to model rail but am still awaiting my free gift. Like the special edition loco's you guys are all waiting for the payment has been taken but the goods not yet received.