I would lean toward tougher conditions...
That said, supernoodle, your buddy that shot 800 may very well have a point.
If you can't practice on the tougher conditions, there's no way you can be ready to compete on the tougher conditions. If nothing else, from a confidence level.
Folks on this board say that you can practice different lines on a house shot - and that is certainly true. What a tough shot gives you is IMMEDIATE feedback - not just on hitting your target, but ball speed, quality of release, and all those other things that make a good bowler great.
I thought I could practice tough shot bowling on a house shot, too. But I found out differently in competition. Very expensive competition. This summer I'm ONLY bowling a sport league, and practicing on tough conditions (preferably sport) whenever I get a chance.
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All things are difficult
before they are easy.
---- Thomas Fuller