There's a bit of pain depending on where you inject. I have issues with Tren in my quads for some reason.
As for the 2nd question: Some people will disagree with this, but everything I've read says Tren Acetate is the most powerful steroid, period. My personal experience is likewise. I "feel" Tren Acetate within the first 5 days. Enanthate takes 2-4 weeks to kick in.
Most people prefer Enanthate simple because they only have to do it monday and thursday. But Tren is harsh and it's better for your levels if you do it every day or every other day. I take 100mg of Acetate every day and have no big sides. But when I took Enanthate at that level, putting 400mg in at one time twice a week, i got mad sides from having that much go in at one time.
Personally I prefer Acetate. And everything you'll read from a drug profile will tell you Acetate is much more powerful.