boldenone undecylenate or eq can aromotize but will do so minimally so will only be noticed when higher amounts are used. Even at higher doses though, aromatization is very small so the side effects that you will get on this are not so common (increase in estrogen through conversion will water retention, female fat distribution, possible gyno). That was not so common problems and I doubt you will have to worry about anything. To be absolutely sure always have nolvadex on hand in case as some people are very sensitive to small changes in estrogen levels.
It is used by people who prefer the hard, more vascular look. Gains are solid and almost always permanent providing you restore your hpta efficiently and quickly. If stacked with dbol (an androgen) you will experience some good gains in both strength and size as eq is a strong anabolic and when stacked with androgen you are getting gains through different pathways.
Deca on the other hand is a good steroid for both bulking and cutting, again it is a powerful anabolic so for best results combine it with an androgen. Deca will not aromatize in to a simple estrogen that can be combatted by using an anti estrogen or anti aromatise.
RU 486 Is your only true safe way to go on deca. So if you want to have something on hand (such as nolva in the case of estrogen) then RU 486 is the way to go, it is very expensive and hard to find. So if you do start getting progestin related side effects then you are pretty much left with them until the deca is out of your system and still it is not completely elimintated and can remain for a long time. Mine managed to leave me fully after about 3 weeks.
My choice would be eq over deca, it is also cheaper which is an added bonus.
Peace
ps if any of this does not directly answer your q, I just c+p'd my answer to a similar question yesterday