I think that my favorite doily of all time is the Dresden tatted doily by Roger aka Freedman. Its very simple to make and tats up quickly. I made 4 of them in 2 months a few years ago for a friend of mine. I altered it a bit by adding beads to the picots on the outside round and Nina Libin style bead leaves periodically on the outside round. I don't have any pictures of the ones I made and I couldn't copy the picture over from Needle tatting two but here's the address: http://groups.msn.com/NeedleTattingTwo/dresdentatteddoily.msnw
Take a look, its a very easy doily, you can make it as big as you like and it looks lovely when finished.
How do I assess the difficulty of a doily? Well, I take a kiss (keep it simple silly) approach to tatting so when I assess the difficultly level of a doily I look at a few aspects of the pattern:
1) basic techniques required- anything with plain old rings and chains I consider easy, start adding in split rings, SCMR, clunnys and you are looking at a different level of difficulty whether you are comfortable with advanced techniques or not. I'm very comfortable with many of these techniques but its just one more thing to think about. I recommend that if you are not familiar with a technique in a large pattern that you practice the technique first. It really sucks to finish a pattern and realise that there's a big difference in quality between the split rings or clunnys you started making and the ones on the outside round. However, I don't believe that advanced techniques alone make a pattern difficult.
2) length of repetitive elements- if you have to constantly consult the pattern because the repetitive element is too long to memorize then its more difficult. You have to keep stopping to check the pattern and you risk skipping a line. This is doubled when the ds counts within the repetitive element change. There's a UFO in my pile that initially looked very very easy. Just rings and chains. HOWEVER, its never going to be finished because the repetitive element is too long, the ds counts change every ring and I keep reading the wrong lines, making the wrong rings and then cutting it out. I'm very bitter about this pattern.
3) number of repetitive elements- when a pattern changes in each section you run the risk of making the wrong element. You tend to get a flow going so its really easy to miss a change or a transition area. If there's 1-2 variations its okay but more than that and it gets dicey. Of course these patterns are impressive once finished so are more than worth the time and patience. What's the difference between #2 and #3? Not a whole lot.
4) the lines of the pattern- huh? well, some tatting patterns go with the flow and curves of the rings and chains while some constantly change direction. This means that you may have to finesse a bit and the pattern may only lay properly once you pin it. It also means that tension may be an issue and you have to tat it very consistently. How annoying if everything is perfect except for one sloppy chain. I never, never, never tat anything without a picture.
This may sound very serious but its not. I'm just sharing one way to look at doilies based on my own experiences. I'm sure everyone will tell you something different and they'll be right. I've had alot better time doing projects once I figured these things out. I don't get frustrated trying to finish a long project in a short time. I also don't have the urge to hurt someone with a sharp shuttle when things go wrong. (my fault? no, never my fault- better to blame someone else) The Dresden doily rates low on all 4 aspects but it looks very nice when finished. Its a good first doily to make.
If a doily rates high in any one of these 4 it doesn't mean I don't do the doily, it just means that I don't work on the doily while watching TV or on car rides. Challenge and change isn't a big deal in a small motif but its a little more serious if its a large doily. There's nothing worse than finding a mistake at the end of a large doily or after hours of work. Believe me that I've done every stupid mistake possible... and some that didn't seem possible at the time. If a doily pattern rates high in all 4 categories then I try to get someone else to make it! That way I can see the results without pulling out all my hair!
However, in a final word there's nothing more beautiful than a well tatted doily, the larger the better. Some of the most beautiful works I've seen were simple patterns done well.