I only have Wilson amps. For a single device consider the Wilson Sleek. They come in a few flavors. The 3g version does all 3g. The AT&T 4g version does AT&T 4g and all 3g.
For multiple devices at one time consider the Mobile PRO 4g. It's pricey.
With the sleek expect 18db gain. The mobile pro 4g expect 35db gain. Do not pay attention to how many bars of service is available. The signal bars are rarely accurate.