It depends where you want to run the freewheel. If you've got it attached to your cranks it's easy enough to get a proper sized cog on the rear wheel. If you run the FW on your hub, be it 16 tooth or worse 18 tooth, it'll be harder to find a set up for your cranks which gives you a decent ratio.
If you can afford it, a free hub is your best bet. You can pick up a second hand hope trials hub for around £60 if you look hard enough. Having that would mean you can have a normal 22tooth front ring and rock guard or an 18tooth set up of that's what floats your boat. Having either of these with a suitably sized rear cog will give you a nice solid feeling drive train.
Having a free hub will mean your chain is stationary when you're not pedalling. So for manuals etc, you won't have an excuse for your jeans being sucked into your chain!