First thing first. Are you using a DTH? If so then is it a HD connection? If YES then are you connecting tv and stb by HDMI cable or not? Even if your connection is not HD, some operators like Reliance RDTV STBs have component cable support. If this is your case, try with component cable. Final thing is SETTINGS. Did you try fiddling with them to make the out put best? Service engineer while installing, did he adjust settings to suit your requirement.If using analogue cable signals, get rid of that connection.
Coming to DTH selection 5 things are to be considered
1.PICTURE QUALITY: HD channels look more or less same on all DTH. What matters is SD picture quality. SD channels look best on Reliance RDTV followed by Airtel, Tata Sky, Videocon DTH...
2.AUDIO: Airtel is the champ. Tata sky closely follows. Videocon also good. Reliance doesn't provide 5.1ch on HD channels.
3.ADDING CHANNELS & EXISTING CHANNEL COUNT: Videocon followed by Tata sky and Airtel. Reliance is hopeless.
4.VALUE FOR MONEY: Videocon, Sun, Reliance in any order. Rest are expensive on their rentals.
5.ADDITIONAL ADVANTAGE:
AIRTEL:You get best Universal remote. Less interrupted by rain than Reliance and Videocon D2H.
VIDEOCON D2H:RF Remote with newer set top boxes offers flexibility in pointing directions. Long term packs are available up to 5 years which offer great value. Offers DOLBY DIGITAL on HDMI unlike rest of them who offer by Optical cable...so helpful for AVRs with ARC. Also no need to buy an optic cable which is expensive.
RELIANCE: Component cable support even in a SD set top box technically gives you HD quality. So you don't need to upgrade for better results.
TATA SKY: offering 3D movies though for a pay by SBS.
NOTE: Didn't discuss about SUN (which is very affordable but poor PQ) and DISH TV (whose PQ is as bad as SUN but prohibitively expensive rentals) as I don't own any of the both.
SOURCE: 2 RDTV+ 1 D2H+ 1 ADTV at my place and 2 ADTV+ 3 TATA SKY at my inlaws place.