The Howa action is a very good action tobuild on ,they are very strong and very rigid ,the bolt is well made being one piece evnted out the side and comes with an awsome extractor being the pined in M-16 style. Now all that said they are a bit short and that can be fixed but it aint cheap due to having a new mag box made or retrofitted so like mentioned above if your building on the 300 Win mag case on down it would be a great action to build on. You are somewhat limited to after marked goodies like stocks and triggers , Timney makes a good tirgger for it and theur are a couple stock makers that inlet for them but nowhere near as many as for the Rem 700 and Savage.
The Savage and Stevens being the same basic animal are very good action to build on for the budget mined folks , they are easy to work on have a reasonable amout of aftermarket parts available. If I were planning to build a custom on one I would set the barrel up wth a shoulder like on the Rem 700 especialy if your planning to go with the bigger cases like the RUM and WSM as they are a bit fatter. You can have they "trued" up just like anyother to make sure that everything is strait.
either way you can build a very accurate rifle off of either , but I will say that if your planning to build a custom rifle
from the ground up and you don't have an action yet then I would highly reccomend that you save a few more dollars and buy a custom action rather than buy a factory action as by the time you inverst all the money into a factory astion to make it smooth and square your not to far for the cost of a custom Rem 700 clone and the custom action will hold WAY WAY more of it value in case you ever have/want to sell the gun. With a Savage custom gun you will basicaly be eating all of the gunsmithing charges and about 50% of the action cost hich will be a big loss on your part.