If you are dead set on getting a Retic i would recommend a main land over a dwarf, dwarf mix, SD, or SD mix as your first one... Reason being is that dwarf mixes and SD mixes tend to be a bit aggressive at first and really flighty... TBH they can be NUTS... I don't mean that in a bad way, just it takes some experience to deal with em and get used to them... I have everything for mainlands to pure SD's so I can speak from experience... Now if you can get PURE SD (super dwarf) or a PURE locale dwarf, that wouldn't be as bad... They are a bit nippy as babies, but are tiny so the bite is no biggie... The other thing about SD's, Dwarfs, and any Dwarf combos is they are FAST as hell, and the love to try to "get away" so it takes some time to calm em down... Mainland Retics do get A LOT bigger when adults, but IMHO are TONS easier to work with as babies, and can be very calm if you get one from a good reputable breeder... If you don't think you can care for a 20ft + snake one day, and again are dead set on a retic I would recommend finding a older Dwarf or SD that has been worked with well and calmed down... It is gonna cost more, but you get what you pay for! Hope this helps...
If you are interested in anything let me know... I have a few things available, and have a friend that breeds pure SD's...