Welcome.
When it comes to guns, especially if going to a brand you have never used, the biggest concern is going to be ergonomics. Handling- Handle placement; mid-handle, rear-handle or something in between. Barrel shape; wide and flat, tall and skinny, round barrel, double taper, single taper, etc. Unfortunately if you have no experience with the brand, there is no guarantee that it will be to your liking.
As far as trigger mechs are concerned, I would recommend a brand that machines all the components out of stainless steel, including all the pins. Do not get cast or plastic components. They will break.
If you can only have one gun, I recommend something that is versatile in configuration. Meaning it will accept a wide variety of shaft diameters and has the capacity to accept multiple bands; a band slot rather than individual holes.
Another aspect to consider is the handle. There are a few gun makers that use the AR-15 style handle base that will allow a multitude of handles to be emplaced on the same base. As of now the only guns that accept these bases, as far as I know are wood custom guns. This base will give you options for rake, finger grooves, girth, length, palm swell, etc.
Your best bet is a custom made gun.