[What makes one viewer give more lag than the other?]

I use Imprudence viewer only, because it has the least lag for me. I can't use Phoenix because everything is all greyed out and the lag is horrible for me.  I'm on a laptop.  My laptop is fairly new. Only one year old.  I purchased it with the best graphics card Dell computers sells. It's frustrating to hear people on laptops that paid $400 for it when I paid almost $5K and have terrible lag most all the time!  What causes this?  Thanks all :D