For me, it depends on what I'm burning. But I do tend to use at least "medium-quality" discs (I will use the high-quality ones for very important data that I can't afford to lose). Generally speaking, the brand of the media does not tell you everything about the quality of the disc. This is because 90% of branded media is actually made in a different factory and the branded with the company name. For example, Sony CDQ74 media is actually made by Taiyo-Yuden of Japan, which has quite a remarkable reputation in making high-quality CD-R dyes. Much cheaper media like Memorex is often manufactured by CMC Magnetics, who have historically made bad media.
However, like Radarman was saying, a quality CD-R drive like a Plextor can burn most (even cheap) media with little or no problems. The quality of the drive will determine a successful burn more so than the quality of the media used.
I will stress though that when shopping for quality discs, quality and cheap almost never mixes. You get what you pay for. All media I've burned with my Teac CDR56S has come out alright, but these are the discs I have particularly liked:
Kodak Digital Science (Kodak) EXPENSIVE
Maxell CDR74 (Hitachi-Maxell)
Ricoh Platinum (Ricoh)
Sony CDQ74 74 min (Taiyo-Yuden)
Verbatim DataLife Plus 74 min (Mitsubishi Chemicals)