I shopped the F-30 and the F-50 extensively over the last couple of months. I currently play a DC-3. The F-30, as Hal said (to my ears at least) is definitely more chimey, but it also definitely lacks the headroom of the F-50. The lead channels are a bit different to my ears too. The F-30 comes really close to the DC-3, but seems to lack the fullness that I was looking for. I would think it would be a great amp for home-studio use. For me, the F-50 is exactly what I was looking for.
What was fascinating to me, and once I figured it out it seemed obvious, was that when you test drive these amps you need to set them up on the floor, not in the shelves that they use at places like Guitar Center. The first time I tried the amps out, I was in a GC and both amps were close to ear level when sitting down, and housed in what amounted to basically isolation boxes that prevented any sound from coming out the back of the amps, with foam padding all the way around and underneath. This is an extremely unnatural way to listen to what the amps can do, and as a result, at first I didn't like either of the amps at all, and I thought Mesa had truly bamboozled everyone into thinking they had a good product.
SO, I started looking at all sorts of other amps. None did it for me - THANKFULLY!!!
So, about a month ago, I was back at the GC trying some stuff out, and decided I'd give the F-50 another go. This time, there was one sitting on the floor in front of the display boxes. I plugged in, and within about 3 seconds I knew I had found the amp I was looking for. Something magical happens when you get these amps set up the way you would usually have them set up - i.e. on the floor. I think there's a definite and appreciable change that happens when the cab is sitting on the ground, because the bass is fuller, and you get to hear that 3-dimensional thing these amps have - the sound seems to be coming from everywhere. You don't hear that at all when you play the amp in the display set-up at these shops.