This is a great question that we touched on before and did not come to a conclusion. Has modern science (which produced the bulk of new steroids in the late 60's, 70's and 80's) given us safer chemicals to work with? And can we improve HRT programs with them?
To begin, we must agree on "safe". I would take this to be some measurement of damaging side effects usually androgenic rather than anabolic. Even this is arguemenative given that a side of anabolic can be the shutdown of the natural test producing system.
Let us assume that at 100/100, testosterone at a low dosage is safe for long term use. In my program, that would be no more than 75 mg p/w total.
The deca drops the androgenic sides risk; 37/125. However, it seems to produce impotence, which is very bad.
The winstrol also drops the androgenic sides risk; 30/320. Now you have stress on the liver.
While the newer chemicals seem to give us more of a mix for cycles for goals beyond restoration of normal within range test levels, I'd stay with test e, c, p or bio-identical for HRT.