I'd go for utility spells that have at least a 10 min/level. There's plenty of spells that could be useful for a rogue but ultimately the usefulness of any spell will be dependent on how you play and what campaign you are playing. It is also worth considering any other spell casters in the group and how you might be able to fill in a small gap. It might be worth checking out alchemical reagents and addition spell components as you can use these to increase the effectiveness of a spell e.g. magnesium grants +1 caster level to transmutation spells for the purpose of duration.