Which ammo is better is like Chevy vs. Ford.. everyone has an opinion... but for a relative inexpenisive ammo try the ones close to M193 spec.
The Federal American Eagle (55 gr - stock # AE223) is suppose to give good accuracy and be reliable.
In my new rifle I shot the AE and winchester USA white box Q3131 and got better accuracy out of the Q3131 than than AE. At 50 yds i got 5 shots all touching.
The Q3131a (again winchester usa white box brand) made in Israel is suppose to be better than the usa made Q3131. Both are to M193 spec. I havent had a chance to try the two boxes I have yet though. But based on my good/accurate Q3131 experience, I will probably use one or the other for now.
There is quite a few comments on bad experience with the Q3131. I think that it was lots made a few years ago though. Out of the 140 rds i shot there were no failure to eject/feed or blown primers. i am going to buy all i can if i find it again for under $4
My local walmart had (i got the last two boxes after buying 5 other boxes earlier, and no other walmart i have been to carred it) the Q3131 for $3.97/box. I found the AE223 and Q3131 at a local gun shop for $4.99 a box.. Ammoman.com/cheaper than dirt/the sportsmans guide all carry one or both of these at good prices (just remember to add in shipping).
The South African also comes recommended as a great plinking ammo. For about $40 you can get 300 round battle packs, 1980's mfg and is close to M193 spec... I havent gotten into my battlepack yet though, but that day is drawing close..
hope this helps based on my experiences..