Inheritance Tax - because it disproportionately effects those who die unexpectedly which adds to the trauma of sudden death. Those who have time to plan can largely avoid it. I also disagree with double taxation in any form.
Stamp Duty - it is strangulating the housing market. I think there should be exemptions for individual private residences in line with Capital Gains Tax but should still be payable on second homes or buy to lets, etc.
Council Tax - it is a huge extra tax paid out of taxed income. It should be abolished completely, councils streamlined with standardised national rather than local policies and the costs added to national taxes. There is too much local variation and 'interpretation', especially in planning rules.
National Insurance - again should be abolished and costs added to income/corporation taxes. If this was achieved, in future years the arguement that pensions are contributory would disappear and the public would accept that they are a benefit so only those on low incomes would be entitled. Reform of NI and pensions needs to start now as it is slow to change.
VAT - I think we need differential rates. True luxury items and those considered harmful in some way should be taxed at a much higher rate to impact the most wealthy. For example - long-haul flights, luxury yachts, private airplanes, super-cars, maybe even champagne! Utilities and other essentials that are taxed should be taxed at a much lower rate, say 10% instead of 20%. It should largely be an optional tax on spending that doesn't unfairly impact the lowest paid.