Minimal bruising is normal and usually isn't anything to worry about.
On a side note. Did you doctor tell you how high your natural T was? When I first started, mine was extremely low (43 >___O; ) And I used to bruise ALL the time, I'd wake up with bruises. But anyway, my point is that if your natural T is really low, you might bruise the first few times that you inject until your T gets up there higher, I know I did.
Also, about the gauges. Well, I used to use a 25g and I could draw it up just fine (If you're not familiar with needle gauges, higher numbers mean that the needle is smaller) I've switched to 22g though. As for pain-wise, I don't feel much of a difference now. The biggest difference was how long it took to draw and inject. A larger needle is going to mean that drawing and injecting is faster, which was why I switched needles, the 25g was so thin that injecting often took longer than a full minute due to my dose. I've been told repeatedly that smaller needles hurt less, however, they're also harder to push into the skin.