8 track
I just switched over from a 4 track cassette to a 1/2" 8 track reel to reel tape deck (Tascam TSR 8), and there is definitly a difference in sound. The reel to reel not only has more tracks but the sound is 'bigger'. There is more presence. I had to go out and buy a seperate mixer, since
the TSR 8 doesn't have a built in mixer, like the portastudio. It simply has 8 line ins and 8 line outs. All 8 always play back, but on the recorder you can select which of the 8 you want to record on. In order to avoid plugging and unplugging, you'll need a mixer which can support that. I bought an 8 channel mixer which also has 8 dedicated tape returns, so it works quite well. When recording, I just turn up the tape returns of the tracks I want to play along with, and push the record button on the reel for that track.
I will say this though, there were certainly hidden costs (al least to me) that showed up. For one, you need cables. I went the low budget way, but it still cost me $70 just to hook the mixer to the recorder. The tape is a major difference. I used to use the Maxell XL2 60 on my porta studio, which cost like a buck for 20 min of record time. THe 1/2" reels, however, at my local music store, cost $48 for about 30 min of record time! You can get them through the internet for less ($35 or so), but still. I find that I don't just let the tape roll and mess anound. I have to plan things out a lot more. Also, if your deck has been used a lot, it may need a head alignment or relap (for my machine, about $300).