Pastels are an excellent "base morph" for people looking to breed for fun and to learn the ropes. They have been crossed with nearly every other morph out there (recessive, dominant, and co-dominant alike).
Unless you have a huge budget you won't end up creating anything that no one else has.
However, I personally think that the Pastel gene enhances the appearance of nearly everything it touches. You really don't have to worry about picking up the wrong morph to cross it into. Figure out your budget and do a little research online (for photos). There are all sorts of sites that have photos of the many various genetic crosses that have been done.
Find a cross or two that you like and then see what fits into your budget. However, a word of caution: don't buy a morph just because you can afford it. Find the morph or combo that you REALLY like and save up if you have to. You will get far more enjoyment out of a project that you like (or love) than one that you can merely "afford".
When you do settle on a certain morph (or two), again, don't just buy the first one you see that you can afford. Breeders will have varying prices and it pays to be picky. It's your money (and time and energy) after all. So look for the absolute best looking example of whichever morph you are interested in.
With quality breeders you will not only be happier with the results of their offspring but good looking hatchlings tend to grow into good looking adults.
Also remember that if you pick up a female hatchling you may have to wait as long as three years before she is ready to breed. (Yes, some can and will breed sooner, but you'll feel less pressured to get her to breed if you realize now that she may take longer to mature.) You can usually find an older female to less your wait time, possibly even a proven breeder, but you will pay more for her than you would a hatchling.
When I purchase a new snake (regardless of species) I always prefer to purchase a neonate over purchasing an adult or sub-adult. I may have to wait longer for them to mature before I can breed them, but I've found that older, more established animals can take longer to "settle in" than the younger ones. In the past when I've purchased adult or sub-adult females I've actually had some of them take as long as a year or more to settle in enough to actually breed for me even though they had both the proper weight and age to breed.
There is a lot to consider, but if you take your time and weigh all of the factors you will be much more content with the results no matter which morph you decide upon.
Let us know what you end up picking up and post some pictures too if you can!
If you want, if you tell us what your approximate budget is, we could help you out by letting you know some of the female morphs that are within your price range.
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Stay United!

"...I say 'apparently' because despite all our progress she is not at all a tame or handle-able snake and gettting her from that cage would re-start a war.. and we've had a good armistice for several months now."-Gus Rentfro - I love this quote!