Reel to reel

2-track 1/2" tape at 15 inches is amazing. But be forewarned- you won't want to listen to 1/4" tape after that...
1/2" 2-channel is a common mastering format.  

Atmasphere is quite right. I only have a handful of 1./2 inch 2 track 30 IPS masters -stunning. But a 1/4 inch 2 track 15 IPS tape with Dolby SR comes pretty close.

- I just down-loaded 4 of the 15 IPS reels that I had recorded to my hard-drive. They really sound good on play back, and I don’t have to get up and put another reel on.

It also saves wear on your repro head, as well as the rest of the transport.

But personally I can’t see why you would want to use R2R to record your LPs. At 15 IPS, you’ll need 2 pancakes of 1.5 mil tape or 1 pancake of 1 mil tape for each LP. Each pancake is GBP35 over in the UK (presumably about USD 40-45). That buys you 2 x 45 rpm QRP pressings of every album.

I do get R2R as a concept - I have 5 studio machines - 1/2 inch 2 tr Studer A820, 1/4 inch 2 tr Studer A807/II, 2 x Sony APR 5000 series and an Otari MTR12. But I play studio masters or dubs. The difference then becomes compelling, although the outlay is very substantial.