I prefer to enter everything to a fixed beat, then alter it afterwards for tempo changes. I might do it differently if the tempo changed greatly numerous times, but I think that\'s best if you\'re talking about gentle rubato type changes.
Whatever you do, do not quantize 100% across the board. That\'s one way to quickly turn your beautiful GPO orchestra into an ugly synthesizer. I use some quantization, as I\'m not always the most accurate player. I just make sure I don\'t overdo it, and often add a slight random shift to each note during quantization (easy to do in most sequencers).
It\'s a very simple equation:
People do not play perfectly. Therefore, perfectly-played music does not sound like people.
There is so much difference when you play your parts. Then, suddenly, you have an orchestra made of lots of instruments, you can feel its size just because each instrument is doing its own way, and not playing chords in a block.
I almost always do the initial rough draft to a fixed, inflexible beat, and then go back when it\'s done (or at least a large section of it) and modify the tempos accordingly so that I can get a sense of how the sound moves and flows. If I were to try to anticipate it before I really see how everything works together I\'d end up changing it all anyway so I figure why waste my time. Maybe others are better at the big picture while they\'re working than I am, but that\'s my system.