First off, welcome. Glad to have you aboard. You'll find lot of friendly and VERY helpful folks here.
Now as far as guns, you should get a ton of comments with that one. LOL
Everybody has their favorite and can share info. Look in the Reviews area of the forum for a little more insight into the listed guns. There you can find some interesting evaluations members have posted.
Both of your Gamo guns SHOULD produce fairly accurate results, depending on the ammo you use and also depending on there being NO hidden issues like a bent barrel or a defective scope. Also make sure you swab the heck out of the inside of the barrel to make sure it is clean before attempting to sight in. Are you using a glass or iron sights? What pellets are you using and have you tried a variety of brands and weights? Each individual gun seems to have it's preferences. You have to find the one they like most.
As far as the guns you are debating, I can answer on the Benji Super Streak. I recently bought it and immediately ordered replacement parts, tore the gun down and did a tune job on it. From the box, it needed some major attention. The lubrication from the factory was what I considered less than minimum. The piston seal was defective, again, right from the box and not being shot by me first. The barrel took about 30 minutes of solvent and swabbing to get it reasonably clean.
With all the bad points out of the way, after I replaced and lubed all internals with the recommended moly and reassembled, this is a tack driving .177 air rifle. I also replaced the heavy trigger with a GRT III, the best $32 anybody can spend on an airgun improvement. I like the heavy weight of this gun that absorbs recoil. The long barrel, IMO, results in a more accurate piece. I hunt with Gamo Rockets (9.6gr) and this gun can definately produce a 1 shot 1 kill scenerio. I just contacted Crosman and am ordering a .22 barrel for it also. At $15.65 + s/h I'll have both calibers to tinker with. I like the gun very much and it's very accurate, depending on the handler of course.

It DOES need some cleaning and tuning out of the box but hey, MOST guns from the factory do. At least to make them more consistant, more enjoyable to shoot and to definately make them last longer.
Buy a Benji SS if you want a heavy weight accurate powerhouse of an air rifle, but I'd also suggest taking a closer look at the ones you have to see what's really causing the issues. Might start with a chrony test. Hey, if you wanna sell tem, just let us know in the classified section. Could help finance the Benji or the next addition to your arsenal.

Happy Shooting!!!!
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