SCSI CD-Rs are better because they don't need a large chunk of your CPU's time to transfer the data to their cache. Because the CPU needs of SCSI CD-Rs are so low, you can basically defrag your hard disk while burning a CD (I've heard of that being tried - on a test burn mind you). Basically SCSI burners let you keep using the computer while the CD burns.
IDE burners work perfectly well, but it's advisable to close all other programs and leave the thing alone while it does its job. For a 2x burner, this can mean leaving it for an hour if you do a test and create, or 35 mins for a normal burn. If you don't have a SCSI card already, IDE will be significantly cheaper for you. If you're not going to use it much, IDE is probably ok.
Personally, I don't recommend buying HP for ANYTHING. I bought a HP CD-R and it died after about 3 CDs. My Ricoh one is much better.
Better yet, if you already have a SCSI card, create your disk images on a SCSI HD and then burn to your CD. The processor time is so negligible that I usually go play MotoRacer II or soemthing while the CD burns.
I'd also stay away from Phillips burners. Mine works great, but apparently I'm one of the lucky ones (and I flash upgraded as well).