I have never used Lightning, but I have a Dixiesys reseller account (mainly for personal stuff) and have never had any problems. I think they got a little backed up with new orders yesterday due to the fact they had to bring another server online due to the flight from you know who. I am not a real support heavy account so all the help and or questions I have had were handled in the forums.
Kit, I have no knowledge of Dixie, but I know the guys at Lightning quite well, and I would urge you to try them first. I use them, and I know that they are not overloaded, have no intentions of becoming so, are online 24/7 to help you, and (here's the icing on the cake), have a 30 day money back guarantee. You basically have no reason NOT to try Lightning first. If for some unimaginable reason you were not satisfied, you take your money back and give it to Dixie. I am confident that won't happen, however.
In short, give Lightning a go, you won't be sorry.
gary at dixiesys is great. totally reccomend him. ive dealt with him in the past and his work is top notch and his is as honest as you could ever ask for. gary must be at least over a year i think as he was around well before i was and helped me in setting up and i was starting last sept \ oct.