I have taken both orencia injections and orencia infusions. The injections do nothing--I feel very few effects at all from them. The infusions are much more effective for me. Maybe because at the infusion you get teh entire dose at once, but the injections you get a small dose every week. If you have a choice, I would recommend you try the infusions over the injections. My rheumy said some of this other patients had the same experience as me.
So far, I like orencia--it's much better for me than the TNF inhibitors.
Best of luck with it!