I beleive also that they are just about even in regards to side effects, although some of the sides differ and one's disposition on whether they are prone to certan side effects will make a big difference. So there really is no definitive overall answer as it is truly an individualized problem.
D-bol is 17-aa and is somewhat harsh on the liver, although the hepatoxicitiy is highlty overrated in the majrotiy. I've used D-bol several times for a period of 8 or more weeks with little elevation in liver enzymes. D=bol aromatizes quite readily to estrogen and can cause excessive fluid retention, whereas tren doesn't aromatize at all, but does have mild progestenic properties that can cause gyno for the few who are prone to it.
Tren also having proesteinc effects will in almost all cases decrease the libido, since endogenous test levels will drop with exogenous androgen use, but exogenous test levels will not rise with tren alone, so it almost always should be stacked with test. D-bol has been known in most to either cause an increase in libido, or have no effect whatsoever on it.
As far as hair loss is concerned, they are both highly androgenic and can accelrate hair loss to those who are predisposed, so if you are in that unlucky category, an anti-androgen such as topical spirinolactone can be fairly effective at combatting hairloss. As far as tren being harsh on the kidneys, I'm convinced this is pure speculation that has taken on mythic status, as there have never been any documented medical reports proving this.