Well, i ride Merida 901-16 (2004 year model)- for money it comes its fine bike. Riding Trek you have to pay for Brand and that sucks (to me). But, as i live in eastern europe, i would pick Trek because it has eylets on frame and fork for mudguard (fenders) fittigs, which is "must have" if you plan winter riding there. Price diference you mentioned is steep (maybe look at 1.2), though and if i would not need mudguards i would pick merida.
Putting Tiagra RD, instead of Sora RD (on whole sora group) is pure marketting- that makes you think that this bike will be better than that 100% sora one. Dont buy on this. Sora RD will do just as well as tiagra i gues.
Regarding sora quality- i have done ~10000 km on my sora with no problems yet, so i think its reliable. Get it adjusted right, look after it- and it will work for years. By time you will know whenever you need better (more expensive) groupset (and which one) or not.