soldering iron

I use the adjustable Weller model # WLC100. Adjustable 5 watts to 40 watts.

Things get much trickier when soldering to terminal posts.You need a high wattage pencil for this preferably 60 watts chiesel type,or a soldering station that can go up to 1200 degree F.If you were soldering at any other location the wattage and temp. is not as critiical.If you need to apply a resistor to a terminal you really have a big risk for a cold solder joint because a terminal requires so much heat to form the solder properly.You have so much more metal to properly heat up.It's just something I've learned from my years of soldering.You need alot of wattage and heat at this particular location IMO.
Good Luck and be Patient and Careful.

If you need a reliable soldering iron, probably the best option for you is a mini soldering station https://toolboom.com/en/mini-soldering-station-goot-px-601/ like Goot PX-601 – it is almost the same size as a traditional soldering iron, but it has an option of temperature adjustment from 250 to 450°C. 80 W power should be enough for most applications. Great Japanese quality and it looks stylish :)

Any soldering iron can go fine. It depends on your soldering skills. You can grab a great solder under $20 as others mentioned. Get some solder iron cleaner as @kosst_amojan mentioned. Get a soldering station as well. It works more professional.