I will try to explain my way of finding decent map, but it's not easy task to find one.
First of all, ideal is to find Pit entrance that is as close as possible to Outer Cloister. Note that it can be just a little further if you can easily reach it with teleporting trick when you open character screen. I saw some players have map where Pit entrance is close to Black Marsh waypoint, so you can try that too if you want.
When it comes to Pit itself, there are few tips how to find good map. You want map which is small and has as many bosspacks on it as possible. Easiest way is to see what is Pit 2 level like, there you can find map where 3 bosses spawn frequently and 4 bosses sometimes. Good Pit 2 means Pit 1 can have less bosses to still maintain good average number of bosspacks. But that is not a rule, just a tip. I have good map with average Pit 2 just because Pit 1 is great, but it's very likely that difference between great and fantastic map is in Pit 2 area. It is a big deal if you have 2.8 bosspacks average there instead of, let's say, 2.2.
In the end, you want map that provides good average of both Pit 1 and Pit 2.
When it comes to map shapes, they are not crucial, but are often very important. You don't wanna map where you have dead ends and need to return back to cover common areas where bosspacks spawn. However this doesn't mean that map where you need to do that is not good. I had pretty good Pit map where I had quite large dead end and have to teleport back a bit, but doesn't matter cause common bosspacks there covered time lost. But, in general you want as few as possible dead ends on map, mostly trying to avoid them if you can. Please note that dead ends I talk about are those where bosspacks frequently spawn. On many maps you have big dead end where bosspacks don't spawn at all, you will naturally skip those.
Also, map with good shape is desirable so you can run it easily without map turned on. But it's not really important, you can get used to anything with good amount of running. So, you asked do I look for certain shape map? I don't, most important thing which defines good map is seconds/bosspack ratio. The lower, the better. This is what I look for and it doesn't matter do i have dead ends on map or is map bad shape as long as this ratio is great.
Now, harder part of searching for good map. It is good idea to run map 3-4 times to see is it potentially good or not before rerolling. It really comes down to experience to determine what can be potentially good map, but it's not hard. If you find map you can run considerably fast and has many bosspacks, you found potentially good map. In 10-20 runs you will see does map fit in. Sometimes you will find map that has many bosspacks first few runs, and then it starts to sux.
Next step when you find something that seems fine, you have to measure your running times and count bosspacks as you run. That will give you seconds/bosspack ratio you care about. How many runs? Impossible to tell. Sometimes I see map is not good as it seems after 15 runs, sometimes I see it after 25 runs. It would be ideal to do at least 50 (or 100 if possible) test runs to determine how good map is cause some maps can remain "bad" for over 30 runs, and rest 70 runs be great. Bosspack number vary as you know. However I tend to believe fantastic maps can't sux for more than a 10 runs.
When you do test your map, pay close attention on areas where bosspack spawn. It is not important to visit ALL areas on map where bosspacks spawn. On every single map I skip 2-3 areas where boss spawns once in 10 or even 30 runs. If it takes time to check that area, then it is very possible it's not worth it and is better just to entirely skip it. It is very important to know your map well to know what is your best teleporting path on it. You can improve efficiency with over 10% just by skipping areas where bosspacks rarely spawn, and you lose too much time checking it every run for nothing.
Summary is, most important thing on map is seconds/bosspack ratio. It takes time to determine is map good or not that way, but is only way to do it, unless you have great evaluation based on experience. Sometimes I rolled map that looked great, and after measuring that ratio it turned out only good, not great.
Also, fair note. Bigger average bosspack number usually means better seconds/bosspack ratio, but not always. For example, I had 7.5 bosspack map on my poison nec, and he was way more efficient on map with 6.5. Not all maps are suitable for all characters. Poison necro prefers maps where bosspacks spawn at one place, preferably in devilkin nest, but pit berserker prefers map with Well and hates map where bosspacks spawn in devilkin nest. So, seconds/bosspack will determine what map is great, not her shape or average bosspack number.
If you want to find some godly map, expect to spend hours and hours rerolling maps to get it. Decent map on the other hand is easier to find.