Depends on what you want and how you respond to them. Halodrol (helladrol) is a tried and true prohormone that was arguably the best all around prohormone ever brought to the market. A buddy of mine was talking to Rich Gaspari at the Arnold the year it came out Rich was telling him get this while you can because it is truly amazing and it won't be on the shelves for long.
Now overall size of course your superdrol, M1T, and Alpha 1 is going to be best. However all of these are very harsh and come with a price when you take them. Personally I would just get some dbol rather then take any of these since dbol at least wont make you feel like garbage.
As far as ones that were effective that are no longer available, androstenedione worked well for many, boldione was a good non methyl to stack.
Epistane is a one that is a hit or miss size wise, some people gain a lot others not so much. However it will harden you up and dry you out very well.
As far as strength gains Dymethazine is pretty good for this as is superdrol. When I ran dymethazine I didn't see so much in the size department but I did get hella strong and kept a majority of the strength gains. The only major side effect I saw was lethargy however it was a manageable lethargy.
Now as far as the non-methyls available today for stacking you have 1-AD, 4-AD, hexadrone (6-mdrol) and stanodrol.
As far as strength I believe hexadrone or 1-AD would be the best for gains while 4-AD is more androgenic and will harden you up more. Stanodrol is really cool because its basically a cheaper proviron.
Hope this helps