Depending on who you ask, the desired filler for 4130 is ER70S-2, ER80S-D2 or even 312 (stainless). Most seem to lean towards the ER70 because of it's slightly lower strength and weld qualities. It's not quite as finicky as the higher strength material. The ER80 when mixed with the base metal, approaches the hardness of 4130. The ER70 weld doesn't get quite as hard. The result is the weld has a bit of "give" which can help prevent cracking or breaking in an impact situation without sacrificing strength in a properly designed assembly. I use ER70S-2.

TIG welds on properly cleaned, prepped, and welded joints will be pretty. If not, you need to fix what's wrong.