I own a Chevy Cruze (which is essentially Jeep model Swift). It's the second Chevy Cruze that I owned since 2007 or so. Personally I am happy with the car.
All three cars have a relatively stable second hand market. For some reason, Corolla owners are quoting really high prices these days and Sunny owners are following their tail. But I feel they just being too optimistic about the value of their vehicles.
For your budget, you may get a 2003/4 Swift, 2000/1 FB15 or a 1999/2000 AE110. If you seriously look around and negotiate, it maybe possible for you to get a newer FB15 or an AE110. So age-wise, Swift has the advantage.
Out of the three, AE110 (assuming it's in good condition) will do better in fuel. Spares would be cheaper but you may have relatively more repairs owing to age, if you don't get a well maintained one.
Swift's awkward shape doesn't make it any comfortable for long rides. It's probably the least comfortable of the three. I've been in plenty of FB15s and AE110s. I feel the FB15 is a bit more comfy than the Corolla.
Couple more things about Swift: It's got high ground clearance so it will go in most of the Sri Lankan roads without getting its bottom scratched. Swifts have a known issue with suspension mounts so if you hear a kata-kata noise in your Swift, don't worry. Any decent garage can sort that problem out. When you go to see your Swift, check if it's a 4WD (look whether it's got a differential). 4WD Swifts are generally bad on fuel. Also avoid the ones which have the bodykit, if you plan to drive on bad roads. Swifts which have climate control A/C, Dual Airbags, retractable mirrors tend to fetch a higher market value.