I agree about line being as important as breed. Assuming that you're purchasing from a good-quality breeder selecting for egg production, my take on top five would be:
1. Egg-laying hybrids
2. Khaki campbell
3. Indian Runner
4. Welsh Harlequin
5. Hmmm.... maybe magpies... but there are probably several breeds vying for #5 status...
But again, be sure to ask your breeder whether they are selecting for top egg production. If they're not, then the line can quickly lose its good laying qualities.
Good luck!