In this conflict of propoganda and misinformation I rarely take anyones word for things, and instead will try and check the information myself.
Russian has carried out a very effective tactic of lies and misinformation so far, and anything (and I mean anything) that they say has to be taken with a pinch of salt.
For months Russia have been denying supplying weapons, ammunition and trained merceneries to Eastern Ukraine, then 3 days ago an independent journalist, and numerous OSCE observers, spotted a convoy of tanks, APC's and armed military heading through a Russian border post and heading down seperatist held territory towards Lugansk. Of course Russia immediately denied this (another lie from them) but with independent witnesses and photographic evidence it's only the most easily taken in that will actually believe the denial.
With regards to MH17, you just need to ask yourself a couple of simple questions.
Why would someone want to shoot it down?
What would they have to gain by shooting it down?
It's easy to blame one side or the other as the war of misinformation fires back and forth, but it takes a bit more brain-power to start asking the questions and properly researching the claims and counter-claims.