I use Liggy modified 1.03 on my 4570. I've tried a some other's but my experience is that Liggy's modified 1.03 is as good as it's gonna get with the 4570.
The Nec-4570 is a quirky temperamental beast, but I've come to realize that it's not nearly as bad as some have made it out to be. You just got to work within it's quirks. I bought mine new for $35 us and this is the first quirk you have to learn to deal with. It's not Plexor, its a $35 us drive. That said here is how I get my cheap drive to perform respectably and consistently:
DVD's - I only burn data dvds - for achival backup, software and lots and lots of lossless audio at 16 bit and 24bit. Currently I use prodisc R04 +D 16X. I create an image file in UltraISO (UDF) and use Image burn to burn at 8x. Yeah, it's not the fastest, but I never get DVDinfo quality score less than 93%. Not bad for cheap drive using cheap media. I've never had one fail on me and the process has been stunningly consistent over the past 300 odd disks.
For better quality repeat the above process with TY16x and you will consistently beat 95% in DVDinfo.
The 4570 is the world's pickiest eater, if you find a brand it likes, stay with it.
The 4570 does have one surprising unexpectedly good feature - it's a really good cd burn/reader/ripper. Especially audio cd's. I'm not kidding. I find it hard to get less than 100% scores on Nero CD Speed, even with cheap media recorded at 24x.
Ironically the 4570 mostly works best with the cheapest of software. The only software I use with the 4570 that costs money is Ultraiso. For Dvd's it a must.
However, to burn the images you create with Ultraiso I strongly recommend Imageburn (free!).
For all cd stuff, both audio and data the cdrtools/cdrdao softwares works better than anything I've seen that costs money. Some good choices: Infrarecorder (free) and CDRTFE (free). Both can be found at sourceforge.
Happy (inexpensive!) burning!