I used some really heavy stuff that I "borrowed" from work donkey's years ago. Recently I've purchased some different gauges and I would advise to do the same, selecting what works best for any given application. There's no one size fits all. Also, in addition to rosin cored solder, an investment in a fluxpen works wonders. (I bought a little bottle instead with a tiny captive brush). I've only just found that out too.