For a starting fixie rider, what is there a 'best' Gear inch to start with? Moderatley hilly area. Edit-just got done with the build, a 70's Motobecane 77.6 GI, (46x16/27" wheels/ 165mm cranks.) now a single speed with coasting. This year it will evolve into a fixed gear ride. Thanks Benzo, will look up the skid patch calculator.
I'd start with a 70 gear inch ratio for a while and adjust from there. Then change your rear cog by one tooth at a time till you figure out what works for you. I would stay within 65 to 75 gear inches for most on-road riding. You could get away with 75+ gear inches if you lived In a flat area or were just a beast of a masher.
The problem with fixed gears in hilly areas is that you'll have to spin very quickly when going downhill. Keep that chain tight and your momentum will help on the climbs.
I prefer to ride slightly higher (about 74 gear inches) since I live in a hilly area and want to be safer when spinning on decents. It may take a few weeks to get used to riding fixed, but your legs will adjust quickly, so don't be too hasty to switch things up.
Also, consider the skid patches with your setup. You don't want to have a setup with only 2 skid patches and wear down your tires too quickly. http://www.Bikecalc.com has a good gear inch and skid patch calculator to help figure it out.
There's no one answer: do you prefer to spin the cadence higher or grind out with a big gear? Are your hills sprintable? When you switch to fixed you'll not only have to deal with working hard up the hill, but descents can be tricky as gravity tries to push the cadence up higher than your legs are used to taking it.
I would suggest that you use a geared bike and experiment with which seem to be the best compromise gears for all of your likely scenarios. Pay special attention to which gear you're in and then try to do a whole journey without changing. After a few experiments you'll have got a good feel for your situation.
You can also run a rear wheel with different cogs to allow for a change of heart - many people run with a slightly easier cog on one side for winter, the other side being slightly harder for the better weather months. (I do that, but then generally tend to forget to change and stick with the harder one (48x16, ~80 gear inches) the year around ...)