I love my Diamond d130j. So my suggestion is biased, but it is a very good quality omni antenna. Superior stainless/aluminum hardware-lasts forever. My best distances here in SFO with major hills and stuff, are as far as 60 miles out on vhf/uhf, and up to 12 miles in 800. For omni, that's not bad IMO. Mine is up 50' off the ground.
It also doubles as a noise pickup antenna through a Timewave ANC-4 noise canceller, through an AlphaDelta coax switch for my HF comms receivers. Serves me well.