UA on IAH-RUH is going to be UA/LH from IAH to FRA and then LH onwards, as your primary one stop option on UA. Turkish with IAH-IST-RUH is another possible one stop. Do note that LH and TK still primarily feature business class seating where not all the seats have direct aisle access. TK does have 1-2-1 seating on the 787s and A350s, but the 777s are in a 2-3-2 config, while LH has most of its widebody fleet in a 2-2-2 config, with 2-2 on the upper deck of the 747. LH's new 787s are supposed to feature a 1-2-1 seating config, but that hasn't been revealed yet.

For awards, where do you want to travel with your awards? Airlines have the best availability for their own award flights, so if you say pick UA, then you would have good (not necessarily cheap) availability on your IAH flights, but FRA-RUH would be subject to Lufthansa releasing partner award space to UA, and vice versa if you picked LH, then you would need UA to release partner award space on those IAH-XXX flights.

For upgrades, be aware that complimentary upgrades is mostly a US thing and not so common else where.

You mentioned Qatar, do note that Qatar uses Avios now, so you can transfer avios between Qatar, BA, and Iberia.

You mention that you didn't like Emirates business class -- why? Was it the seating config? What do you value in business class?