Cardas solder excellent sound and has flux rosin built in flows nice , Donot use a solder pen spend $100+ on a good-solder station
+1 on both counts. Cardas solder is actually quite good, albeit not inexpensive (the cheapest source as of this writing is the diyaudio store). Flows well, low melting point, it's a treat to use. Honestly it's not a lot better than the Delta 62/36/2 I used to use, but the Delta isn't that much cheaper either.
I have a 200W AiXun T3A soldering station I really like, it was like $100 including a selection of C245 active tips. Recommended