@Bellebelleagain you received a very good overview from blue345. I would just add, regarding Vanguard versus AJ Bell, that an important criterion should be: would you like to have as many different investments as possible, or would you prefer to have just a reasonable selection with low fees? It really depends how conversant you are in investment choices.
Vanguard offers low fees, mostly passive (indexing), and only their own products. Because the parent company is effective a mutual, not owned by for-profit shareholders, the whole philosophy has always been to keep fees low. The site also has a lot of financial education materials. I like Vanguard for a person who wants the different tax wrappers, does not want to pay an advisor an annual percentage of assets, is comfortable making their own decisions about asset allocation, and does not need or want to make highly granular choices. I don’t think any of their products are rubbish products, but on the other hand some of their products are probably unsuitable for certain investors, and as they reflect the overall market, some will be unattractively valued at certain times. I have not tried their customer service so would suggest checking online reviews to assess whether they are any good with transfers.
I, myself, do not use the Vanguard platform because I am a retired financial services professional who wants to make highly granular and specific choices, especially when it comes to bonds, where I do not like index funds and want to choose my own bond maturity dates. I also don’t want to pay HL prices, and I don’t like the user interface at Interactive Investor. I am comfortable using a fund search engine to sift through thousands of funds and choose the ones that suit me best. So I would personally use AJ Bell if I were going to use any of these. I would also use AJ Bell over Vanguard if I had existing investment investment funds that I wanted to transfer in without having to sell them first, because Vanguard would not be able to cope with that given their limited set of funds. That would be especially important for any funds held outside of a SIPP or ISA because funds in a general investment account would crystallise CGT liability upon being sold for the transfer to Vanguard.
I personally also do not l like the robo advisors because I don’t want to pay a percentage fee for a semi-automated asset allocation, but that is because I can decide upon my own. If you feel comfortable making and implementing your own decisions how much to hold in stocks, bonds, cash, and “other”, you don’t need a robo advisor. If, on the other hand, you are the kind of person who is likely to trade out of whatever feels bad because it is going down, and trade into whatever is going up due to FOMO, then a robo advisor might very helpfully prevent you from that very common mistake, which is otherwise known as selling low and buying high, which is what a large proportion of individual investors end up doing.
This posting is not a recommendation nor is it advice, in part because I don’t know any other people’s specific circumstances, but it is a discussion of how I have personally thought about what to do myself, in case that is useful to others’ thought processes. I think AJ Bell is perfect for certain people, Vanguard for certain other people, and even HL or Interactive Investors are perfectly good choices for people who prefer them.
A final thought, some of these sites at least allow you to open a paper portfolio to try out the platform, and if they don’t, another option is to open an account with a small balance just to test out the look and feel. If you hate the user interface and it puts you off of investing sensibly or investing at all, then it’s a bad deal no matter how low the fees are.