There are a lot of brands in the market but each has its own qualities. How to pick a good balance between economic and quality paints?
The most expensive doesn't always mean its the best. Some very inexpensive brands deliver a very unique consistency and capable of artist quality results.
Don't pick Pastels by Brand, rather look for shades that best fit your Palette.
How to find the best brand of oil pastels? Try them out. Try as many brands as you can. What's best for one may not do the trick for the next person. What are you looking for? Something to layer and layer? Details? Hard? Soft? High pigment? Professional quality or student? Are you working with children? Adults? What ever works for you, to get the out come you want, is the best for you. Most often you may find scads of different brands on Ebay, for a nice small price. Take the opportunity to give them a go. You might find your "next" favorite.
Also for those oil pastels you do not care far use as your under layers to save on the ones that you like better!