If you have never used tren before, run tren ace. Since it clears in three days, you are not going to be stuck with any real nasty sides for very long should they show up. With tren enanthate, yo end up with the tren in your system for about two weeks and you get to enjoy the sides for another two weeks.
Tren can have some very nasty and very dangerous sides.
Tren ace has been more popular for quite some time, so it is the cheaper of the two. Tren enanthate is in a much higher demand at the moment.
There is no better or worse. Both are tren. Tren ace is more hormone per mg, but it needs to be injected much more frequently. I have used both at similar doses and can say that I get less sides with tren enanthate and I seem to get less of a big "hit" from enanthate.