hydraulic vs solid lifters?

[redlinedeath]

So im not very familiar with top end workings, and have a very base knowledge on cams and cam profiles. so my question is this one: our cars come with hydroulic (sp?) lifters, but everyone seems to convert to solid lifters, or suggest the conversions. on an na build, why is this recommended? Running 10-40 oil, and possibly different(if availiable) valve springs wouldnt be as reliable?

any info (in depth even, i catch on quickly, and if im stuck the internet is a good place to have) would be appreciated. my car died again, this time with massive over heating (melted my ign. coils!) and found fresh coolant in my fresh oil after i replaced my radiator. likely warped heads. so this time, im doing a full rebuild, but trying not to break the bank, parts stores dont exactly pay well...