This is a difficult question, I find something different in all the four magazines. I like the technical input particularly and you can find really good articles in all of the magazines.
I think the standard of the DIY advice and technical strip downs is good in all of them. I do like the style of journalism in LRE, it is good English and interestingly written.
For me I have come to appreciate LROI the most, though I must say their 'Bulletin Board' could do with a work over, the contributions are not as good as the LRE board which I feel apart from its 'difficulties' has really excellent input. Look at the Zuess Gears thread at present for example.
Where LROI excels is in its 'Experts' team, they are all really knowledgable and many of them work or are directors/owners of top LR independents. I have never seen such a knowledgeable team in any other motoring publication.