Translation is a very good point and one I'd neglected. You're right: I'm essentially judging these authors on characterisation, ideas and structure, rather than language, which may well boost Solzhenitsyn and (depending on the translation) depress the others.

The main thing I dislike about many Russian authors I've read is that the philosophical/moral questions they explore are fairly abstract and idealised. Their characters often seem similarly stylised. This definitely applies to Dostoevsky and to an extent Chekov; even Tolstoy, though his settings and characters are more earthy, his big idea about the impact of individuals on history is quite abstract. I'm not saying these aren't important or that many people don't get a lot from them, but personally I don't (at least not to the extent of appreciating a 500+page novel built around them). CP Snow's exploration of melancholia in The Light and The Dark, or his exploration of the shades of grey in moral choices in The Affair or The New Men I find much more compelling.

In Solzhenitsyn, on the other hand, I find the characters much more compelling - for many, one can see oneself (or others you've met) acting in such a way, if placed in such a circumstance. It probably helps that I find the topic he's covering intrinsically interesting (and one challenging to write about well). In The First Circle, I particularly admire his structure - in many ways the novel reminds me of Catch-22 - in which he gradually builds the realisation that all characters are equally trapped and yet have certain freedoms, with the final closing of the trap at the end sealing things off.

Anyway, not trying to say one is better than the other, but hopefully explaining my opinion. Thank you also for the other recommendations - I've had a quick look on Amazon and will definitely check them out.