The "best" vacuum gauge for the pressures you are talking about would be a 100 mTorr (100 micron) full scale capacitance manometer as you will get at least 0.5% accuracy, fast response and the reading will be correct regardless of the gas that you have in the system. Downsides are price (~2 grand new)and the fact that you have to pump to about 10-6 Torr to properly zero it. You can get good readings down to the 10-5 Torr decade.
Getting practical, a Pirani gauge is a good bet. You will have adequate accuracy (25% if you don't abuse it) and good repeatability (5%, also if you don't abuse it). Major downside besides accuracy is gas sensitivity (it's a thermal gauge, it doesn't measure "real" pressure) which means that you will have different readings for air/nitrogen, deuterium, or anything else that you put in the chamber. D2 readings will be off by around 30%. Most Pirani gauges don't read below 1 to 5 microns. Some of the newer gauges with micromachined sensors will go into the decade below 1 micron. Pirani gauges have a fairly fast response, about .1 sec (same as a cap. manometer).
Thermocouple gauges are plentiful and cheap. Accuracy and repeatability are a tad worse than the Pirani and response time is slow, usually several seconds. T/C gauges are also thermal gauges and their range will bottom out at around a micron.
Cold cathode gauges are usable as their ranges usually extend up to 20 to 30 microns and they can measure down to at least 10-7 and the newer magnetron gauges can go to the -9 scale and below. They are also gas sensitive and will display a much lower reading for light gases than for air. Accuracy is in the ballpark with the Pirani gauge.
I have a fair amount of experience with the 3 cfm refrig service pumps. Don't expect one to evacuate a "real" system to much lower than 40-50 microns. They are inexpensive, some are a bit noisy, and work well for backing diff or turbo pumps. I'd not recommend one by itself for a fusor.
Try to get a good 2-stage rotary vane pump. For home use the belt driven ones are great - reliability is good and you can do common repairs (shaft seals, etc.) yourself.
Steve
Created on Saturday, March 10, 2001 4:56 PM EDT by Steve Hansen