in ladder, ppl will use wtv way to steal the ladder points.....too many Zerg players and all uses same strat.

in 1v1 custom game u can practise the map you want, you might meet new friends who likes custom game too, you might meet new practise partners, and you can use it to perfect your build.

Is it a spiking lag or normal consistent lag that you are having?

As I said, not only starcraft 2, its the international link in general. Reconnect to a different ip range (not just ip itself) preferably that you can verify that it's connecting on a different gateway as the one you're having is most likely affected and any ip range under it would be affected