quick synthetic question

My 99 silverado has around 70,000 miles and im thinking of changing to synthetic, is there a better synthetic oil brand or are they all pretty much equal. Second, is it okay if there is still traces of regular oil in the engine (like if i just drained it the conventional way) or does it need to be flushed somehow before adding the synthetic, and if so how?

I use Mobil One 15-50 W in my 98 Chevy Z71, what they use in new Corvettes (not that weight though)My truck had over 100,000 when I bought it, has 147,00 now. Uses no oil.

Mobil 1 5w30...but I live in brrrrh cacacanada....

I switched to mobil 1 at 110,000 miles in my 97 with no probs.

i use Royal Purple (best i have found and not overly expensive) and have right after break in. changed oil after about 1000 miles.you do not need to flush, just drain as usual and install new filter and use a good filter not a cheap walmart filter. does no good to go with synthetic oil to protect better and then use a cheap filter.

Mobil 1 and Amsoil are the best synthetic oil for the money from what I hear.

I've used Quake State synthitic since I bought my 86 Silverado, previous owners used Amsoil. Leaks very little oil, burns none. 158,000 miles now.

I've been using Shell Rotella T 10W30 in my trucks. Yes it's formulated for heavy duty diesel engines but also works very well in gas engines. It's a very high quality conventional oil...if you check out the specs on it you will see that it's cold temp pour point is a lot lower than most 5W30 oils on the market