I'm a bit confused about what visa you intend applying for this week - it doesn't sound to me like you're at that stage yet in the application process.
Regional Sponsored (Provisional) 475 visas can only be applied for after you have obtained a positive skills assessment from the ACS and after you have been granted regional state sponsorship in a state that has your occupation listed on their State Migration Plan (SMP). If this is the visa you have in mind, only South Australia will have much in the way of job opportunities for software developers/engineers as that is the only eligible regional area that includes a decent sized city i.e. Adelaide though Adelaide is unlikely to have many openings. In NSW or WA, work in the cities of Sydney and Perth is excluded from eligibility and there will be very few good jobs in your occupation in the areas that are eligible. The Visa Application Charge (VAC) for a 475 is AUD$2960 and skills assessment with recognition of work experience is $550. You may also need IELTS for the points test - cost depends on where you do the test.
http://www.immi.gov.au/skilled/general-skilled-migration/475/ 475 visa
http://www.acs.org.au/index.cfm?action=show&conID=skillassessment ACS skills assessment
Regional Sponsored Migration Scheme (RSMS) visas are employer sponsored and you must have the employer sponsorship before you apply. Jobs in Perth and Adelaide are eligible for RSMS visas and Perth probably offers the largest number of opportunities for you. Cost to the applicant is between AUD$2095 and $3105 depending on where you apply and the employer must pay a $520 nomination charge. No skills assessment will be required and IELTS won't be necessary if you're from an English speaking country.
http://www.immi.gov.au/skilled/skilled-workers/rsms/ RSMS visa
EDIT:
1) If you can pass the points test for a 176 visa and of course if you can get state sponsorship for that visa, a 176 is the visa you should try for as you can work anywhere in the sponsoring state and are not excluded from the capital city. A 176 is also a permanent visa whereas a 475 is only provisional for at least 2 years.
2) The best states for an IT professional will be NSW and Victoria with WA also a possibility but Perth is a much smaller city than Sydney or Melbourne (its economy is booming though). I'm not sure which of those will process your sponsorship application the fastest but that will be listed somewhere on their state migration websites.
http://www.immi.gov.au/skilled/general-skilled-migration/176/nom-state-terr.htm State migration sites
3) An ACS assessment is valid in all states.