First, to clear the ground a little, some boring background. I don't know who coined the term 'the Uglies' for the Indian States, but it goes back a long way. Probably a Penny Black fancier. Anyway, it refers to the group of Indian princely states that, at different times between 1864 and 1953, ran their own post offices, and issued their own stamps - in most cases, valid only for postage within the borders of the particular State.
Some of the States were very large. Hyderabad had a population about the size of Australia at the end of its stamp-issuing life in the late 1940s. Jasdan at the same time had only about 35,000 inhabitants. Some were long-lived: Soruth was the first State to issue stamps, in 1864, and continued until 1950. Dhar issued its first stamps in 1897, and ceased in 1901. Dungarpur first issued stamps in 1933 and continued until 1948 - largely completely ignored by the philatelic world; Gibbons didn't admit it to the catalogue until the 1990s.
Two things tend to put collectors off the Uglies: their reputation for fakes, forgeries and reprints of all kinds, and the scripts used.
Of course there are fakes etc, but so there are for all the countries in the Top Ten.
You apply the same techniques to sorting out the good and bad amongst the Uglies as with any other country. And Knowledge is Power - you need to know your subject.
The scripts can seem a bit daunting to begin with - but remember, they're all alphabetic. With the help of an alphabet for the particular script you're looking at, you can often make remarkable headway. https://www.omniglot.com lists just about every alphabet known to man, and explains how they work.
So the individual States.
First Alwar:

Alwar is a great little State for both the general collector and the specialist. Most of the stamps are inexpensive and quite available.
For the generalist, there were five basic stamps: the four shown, and a variety of the large blue stamp in green (which is rare and expensive, which is why I can't show it).
For the specialist, there were several lithographic stones used for the first two types, made up of repeated groups of small numbers of transfers, all of which can be plated (stoned?). On top of that, there were three periods of postmarks: small seals in the early days, larger rectangular cancels later, and finally, orthodox CDSs. Some combinations of stone and cancel are rare and desirable.
Next is Bahawalpur, the least ugly of the Uglies:

With the exception of a set of overprints on India at Indian Independence (rare and expensive), all the stamps of Bahawalpur were recess printed by De La Rue, in the best George VI style. Well, the Amir of Bahawalpur was a philatelist ... (The collector's dream, isn't it: to be absolute ruler, able to order and issue your own stamps, with your own portrait.)
Unfortunately, or so the story goes, the Amir was a bit of a man-about-town in London, and occasionally found himself short of a little loose change - so he would phone De La Rues and order up a few more sheets of whatever was on hand. Certainly, most issues of Bahawalpur are very reasonably priced mint.
Used are another matter. These stamps certainly did postal service, but genuinely used are in most cases scarce, and unless you know what you're doing, used and covers are better avoided.
Next up, Bamra and (wait for it) Barwani ...