This one looks very nice and the colour looks great with Paine, as it matches some of the colour on her top.
I would suggest you try to cut out more of the white surrounding Paine, or look for renders on the internet that people have already created so you don't have to worry about cutting.
Otherwise I would try what Shadra said and try to blend more around the character so that it's less noticeable.
The text is simple and clean which is good, but I would suggest placing it closer to Paine as it does distract the audience away from what they should be looking at, which is Paine in this case. =)
Very cute background. It matches Rikku's personality very well. Bright and Happy. XD
Once again the white bits that have been missed should be looked at and even then it would look nice if Rikku was blended a bit more into the background. Don't want her to look slapped on over the top.
The text font is nice, but it should be placed closer to Rikku and the text colour shouldn't be black in my opinion. White would look better. Rikku should probably be placed more into the middle as well. =)
I'm not too fond of the background in this one, but the glow around Penelo looks great! This one is blended better then the previous two as well.
The text font is a little out of place and once again should be closer to Penelo, but you've still done a great job on all of these.
Keep up the great work and it's good that you're experimenting. Not a lot of people like to go out of their comfort zone. =)