Ok, for a great budget gun between the: Maverick 88, Pardner Pump, and the Stevens 320... I would recommend the Maverick 88 hands down. There are 3 reasons why I recommend this.
First is the parts interchangeability. you can change almost everything on the Maverick out for Mossberg parts, except the trigger housing, and the forend (you can in fact change the forend, but you have to purchase a sllde tube assembly first). The pardner pump is limited by the barrel attachment point. It's in a different position as the Remington 870's so barrels don't interchange. Parts for the savage 320 are pretty much Nil, not a whole lot of aftermarket support there.
Second is quality: The Maverick 88's I own (Six in fact, though each has their own role in my day to day life) have all worked extremely well, all of them now have at least 500 through each with my clay gun getting close to 1500 rounds. Their fit and finish and finish is fine, but a little rough around the edges, not as smooth as their Mossberg counterparts.
The pardner pumps I used to own (3 total, 1 of which had to be warranty replaced). The major issue I've had was quality issues with the shell stop and interrupter falling out(they are supposed to be soldered in) and I've also had barrel fit issues causing POI to shoot quite a bit right(This was the gun I had replaced). The finish was... well really easy to scratch up, and liked to rust a bit. the gun itself was built like a tank though quite rough internally( I would cut myself occasionally, trying to clean inside the receiver).
As for the stevens 320, I have not personally owned one yet( I will get around to purchasing one for review I hope)but the big issue they've had(and since fixed) were welds that attached the forearm to the action bars. the older models used to break after awhile.
Third has to do with country of origin, if that means anything to you.
Maverick 88: assembled in Eagle Pass, TX with some parts made in mexico
Pardner Pump: Assembled in China by Hawk Industries
Stevens 320: assembled in China not sure of MFG
Also prices in my area are as follows:
Maverick 88: 188 .00
Pardner Pump: 179.00
Stevens 320(standard stock/field barrel):172.00